Schedule
Monday, 08:3009:00 

Registration / Technical testing 
Monday, 09:0009:15 

Opening words 
Monday, 09:1510:15, A106 

Christian Boehmer 
Modified theories of gravity  foundations and models 
In the first part of the talk I am discussing General Relativity, in particular its basic ingredients and its mathematical structure. This will naturally lead the way to consider various modifications or extensions of General Relativity, many of which have been studied recently. Next I will discuss modified gravity models based on generalised geometries and on actions no longer linear in curvature. The main part of the talk will discuss how these many different theories can be studied using a single unified approach which also shows the equivalence of some of these models. Boundary terms in the action will play a crucial role in establishing the equivalence between different theories. The final part discusses the study of cosmological models using dynamical systems techniques. 
Monday, 10:1510:45 

Registration / Coffee Break / Poster Viewing 
Monday, 10:4511:45, A106 

Francisco Lobo 
Beyond Einstein’s General Relativity: Hybrid metricPalatini gravity and curvaturematter couplings 
Einstein’s General Relativity (GR) is possibly one of the greatest intellectual achievements ever conceived by the human mind. In fact, over the last century, GR has proven to be an extremely successful theory, with a wellestablished experimental footing. However, the discovery of the latetime cosmic acceleration, which represents a new imbalance in the governing gravitational field equations, has forced theorists and experimentalists to question whether GR is the correct relativistic theory of gravitation, and has spurred much research in modified gravity, where extensions of the HilbertEinstein action describe the gravitational field. In this talk, I perform a detailed theoretical and phenomenological analysis of two largely explored extensions of f(R) gravity, namely: (i) the hybrid metricPalatini theory; (ii) and modified gravity with curvaturematter couplings. Relative to the former, it has been established that both metric and Palatini versions of f(R) gravity possess interesting features but also manifest severe drawbacks. A hybrid combination, containing elements from both formalisms, turns out to be very successful in accounting for the observed phenomenology and avoids some drawbacks of the original approaches. Relative to the curvaturematter coupling theories, these offer interesting extensions of f(R) gravity, where the explicit nonminimal couplings between an arbitrary function of the scalar curvature R and the Lagrangian density of matter, induces a nonvanishing covariant derivative of the energymomentum tensor. I explore both theories in a plethora of applications, namely, the weakfield limit, cosmology, and irreversible matter creation processes of a specific curvaturematter coupling theory. 
Monday, 11:4513:00 

Lunch 
Monday, 13:0013:25, A101 

Adrià Delhom I Latorre 
Identification of some redundant operators and a generalized Einstein frame in MAG theories 
Inspired by recent findings involving RicciBased Theories, in this talk I will argue why, for theories reproducing GR at low energies which admit a perturbative expansion for the higher order corrections, and for which derivatives of the metric do not appear in the Lagrangian, the terms containing \(R^{\Gamma}_{(\mu\nu)}\) beyond the EinsteinHilbert term can be understood as redundant operators (in the Effective Field Theory sense) that can be reabsorbed into the interactions of the matter sector. At the same time, the form of the field equations suggests that the metric which describes gravitational perturbations is not the one in the original frame of the theory, namely \(g^{\mu\nu}\), but rather an object \(q^{\mu\nu}\) defined from the derivatives of the Lagrangian with respect to \(R^{\Gamma}_{(\mu\nu)}\). I will then try to outline the construction of a sort of generalized Einstein frame where \(q^{\mu\nu}\) acts as an effective metric. 
Monday, 13:0013:25, A102 

João Rosa 
Junction conditions in Palatini f(R,T) gravity 
We work out the junction conditions for the Palatini \(f(\mathcal{R},T)\) extension of General Relativity, where \(f\) is an arbitrary function of the curvature scalar \(\mathcal{R}\) of an independent connection, and of the trace \(T\) of the stressenergy tensor of the matter fields. We find such conditions on the allowed discontinuities of several geometrical and matter quantities, some of which depart from their metric counterparts, and in turn extend their Palatini \(f(\mathcal{R})\) versions via some new \(T\)dependent terms. Moreover, we also identify some ``exceptional cases" of \(f(\mathcal{R},T)\) Lagrangians such that some of these conditions can be discarded, thus allowing for further discontinuities in \(\mathcal{R}\) and \(T\) and, in contrast with other theories of gravity, they are shown to not give rise to extra components in the matter sector e.g. momentum fluxes and double gravitational layers. We discuss how these junction conditions, together with the nonconservation of the stressenergy tensor ascribed to these theories, may induce nontrivial changes in the shape of specific applications such as traversable thinshell wormholes. 
Monday, 13:2513:50, A101 

Alejandro Jimenez Cano 
Restrictions in quadratic metricaffine gravity from the stability of the vector sector 
In this talk we will revise the stability of the four vector irreducible pieces of the torsion and the nonmetricity tensors in the general quadratic metricaffine Lagrangian in 4 dimensions. This analysis highly constrains the theory and reduces the parameter space of the quadratic curvature part from 16 to 5 parameters. We will also mention the case of WeylCartan gravity, proving that the stability of the vector sector completely fixes the dynamics of the full Lagrangian to just an EinsteinProca theory or pure General Relativity. 
Monday, 13:2513:50, A102 

Aneta Wojnar 
Matter properties vs gravity 
I will review a few last findings related to properties of matter in stellar objects in metricaffine theories of gravity. 
Monday, 13:5014:15, A101 

Damianos Iosifidis 
The Full Quadratic MetricAffine Gravity: Solving for the Affine Connection 
We consider the most general Quadratic MetricAffine Gravity setup in the presence of generic matter sources with nonvanishing hypermomentum. The gravitational action consists of all 17 quadratic invariants (both parity even and odd) in torsion and nonmetricity as well as their mixings, along with the terms that are linear in the curvature namely the Ricci scalar and the totally antisymmetric Riemann piece. Adding also a matter sector to the latter we first obtain the field equations for the generalized quadratic Theory. Then, using a recent Theorem, we successfully find the exact form of the affine connection under some quite general nondegeneracy conditions. Finally we shall discuss the consequences and also applications of our result. 
Monday, 13:5014:15, A102 

Adrián CasadoTurrión 
Collapsing stars in \(f(R)\) gravity 
Gravitational collapse is still poorly understood in the context of \(f(R)\) theories of gravity. The archetypal OppenheimerSnyder model (which is an exact solution of General Relativity) is known to be incompatible with the junction conditions of \(f(R)\) gravity, both in the metric and Palatini formalisms. In this talk, we shall explain how the OppenheimerSnyder construction must be generalised so as to fit within \(f(R)\) models of gravity. By means of a systematic analysis of the relevant junction conditions, we will show that some paradigmatic vacuum metrics cannot represent spacetime outside collapsing stars in \(f(R)\) gravity. 
Monday, 14:1514:40, A101 

Francisco José Maldonado Torralba 
ALP dark matter from torsion 
In this talk I will explain how the pseudoscalar degree of freedom of the quadratic Poincaré Gauge theory of gravity can act as a dark matter candidate. I will give the parameter space of the theory for which such dark matter candidate can account for all predicted cold dark matter, and constrain such parameters based on current astrophysical observations. 
Monday, 14:1514:40, A102 

Shaswata Chowdhury 
Stable Hydrogenburning Limits in Rapidly Rotating Very Low Mass Objects 
We present novel effects of uniform rapid stellar rotation on the minimum mass of stable hydrogen burning in very low mass stars, using an analytic model and relaxing the assumption of spherical symmetry. We obtain an analytic formula for the minimum mass of hydrogen burning as a function of the angular speed of stellar rotation. Further, we show the existence of a maximum mass of stable hydrogen burning in such stars, which is purely an artifact of rapid rotation. The existence of this extremum in mass results in a minimum admissible value of the stellar rotation period of ∼22 minutes, below which a very low mass object does not reach the main sequence, within the ambit of our model. For a given angular speed, we predict a mass range beyond which such an object will not evolve into a mainsequence star. 
Monday, 14:4015:00 

Coffe Break 
Monday, 15:0015:25, A101 

Jorge G. Valcarcel 
New black hole solutions with a dynamical traceless nonmetricity tensor in MetricAffine Gravity 
In the framework of MetricAffine Gravity, we focus on the dynamical role of the traceless parts of the nonmetricity tensor and construct new static and spherically symmetric black hole solutions with independent shear charges. 
Monday, 15:0015:25, A102 

Surajit Kalita 
Gravitational wave observation as a tool for validating modified gravity in white dwarfs 
After predicting many sub and superChandrasekhar limiting mass white dwarfs from the observations of peculiar type Ia supernovae, researchers proposed various models which can separately explain these two classes of white dwarfs. We have shown that these two peculiar classes of white dwarfs, along with the regular Chandrasekhar white dwarfs, can be explained by a single form of modified gravity, whose effect is significant only in the highdensity regime, and it almost vanishes in the lowdensity regime. Thereby it can explain the violation of the Chandrasekhar masslimit of \(1.4 M_\odot\). However, so far, there is no direct detection of such white dwarfs, and hence it is difficult to single out one specific theory of gravity. In my talk, I’ll show that gravitational wave observation is one of the prominent ways to single out the exact theory of gravity. We estimate the amplitudes of all the relevant polarization modes of gravitational waves for the peculiar and regular white dwarfs and thereby discuss their possible detections in the future through some of the proposed gravitational wave detectors, such as LISA, ALIA, DECIGO, BBO, or Einstein Telescope. This exploration links the theory with possible observations through the gravitational waves in modified gravity. 
Monday, 15:2515:50, A101 

Flavio Bombacigno 
Spherically symmetric spacetimes in metricaffine ChernSimons gravity 
We discuss some recent developments for the metricaffine formulation of ChernSimons gravity, where projective invariance is recovered by enlarging the Pontryagin density definition with nonmetricity depending terms. In particular, we show how analytical solutions for the metricaffine structure can be obtained in spherically symmetric spacetimes, by requiring the absence of dynamical instabilities which we demonstrate to be generated by peculiar components of the affine connection. Finally, we present some exact solutions for the homogeneous and isotropic cosmological background and we discuss in details how the propagation of gravitational waves is affected with respect to the metric formulation. 
Monday, 15:2515:50, A102 

Fernando Izaurieta 
Gravitational Waves in ECSK theory: Robustness of mergers as standard sirens and nonvanishing torsion 
The amplitude propagation of gravitational waves in an EinsteinCartanSciammaKibble (ECSK) theory is studied by assuming a dark matter spin tensor sourcing for spacetime torsion at cosmological scales. The analysis focuses on a weaktorsion regime, such that gravitational wave emission, at leading and subleading orders, does not deviate from standard General Relativity. We show that, in principle, the background torsion induced by an eventual dark matter spin component could lead to an anomalous dampening or amplification of the gravitational wave amplitude, after going across a long cosmological distance. The importance of this torsioninduced anomalous propagation of amplitude for binary black hole mergers is assessed. For realistic lateuniverse astrophysical scenarios, the effect is tiny and falls below detection thresholds, even for nearfuture interferometers such as LISA. To detect this effect may not be impossible, but it is still beyond our technological capabilities. 
Monday, 15:5016:15, A101 

Simon Boudet 
Black hole perturbations in metricaffine ChernSimons modified gravity 
The ChernSimons theory of gravity is obtained by adding the Pontryagin density to the EinsteinHilbert action of General Relativity. This additional term is a topological, parity violating term, which arises in different contexts such as quantum field theory, string theory and loop quantum gravity. When the coupling to the ChernSimons term is promoted to a (pseudo)scalar field, the field equations are modified, offering interesting theoretical insights and new phenomenological predictions. In this talk I will consider the metricaffine formulation of ChernSimons gravity, presenting a generalization of the theory in which the symmetry under projective transformations of the affine connection is restored via a modified Pontryagin density, which still retains its topological character. The theory comes in two versions, depending on whether a kinetic term for the scalar field is included in the action or not. However, in both cases, the scalar field has dynamical character, in contrast to the purely metric version of ChernSimons gravity. I will show how the connection field equations can be solved perturbatively for the torsion and nonmetricity tensors, allowing to study the dynamics of the metric and the scalar field perturbations within the resulting effective scalar tensor theory. As a concrete application I will focus on the evolution of tensor and scalar perturbations on a Schwarzschild background. The parity violating character of the Pontryagin density only affects the axial modes of the black hole, whose quasinormal frequencies are modified with respect to General Relativity and the purely metric version of ChernSimons theory. Finally, I will discuss the properties of the late time section of the gravitational signal, showing how a distinctive signature of metricaffine ChernSimons gravity is encoded in the exponents of the power law tails. 
Monday, 15:5016:15, A102 

Sreekanth Harikumar 
Lensing of gravitational waves in Palatini f(R) gravity 
The planned next generation of detectors like Einstein Telescope, Cosmic Explorer and space based detectors like LISA are likely detect gravitational waves signals more frequently than now. With such an increased frequency of detection we expect some of the signals to be gravitationally lensed. This lensing phenomenon showcases some interesting features like diffraction and formation of beat patterns. Another opportunity that lensing opens up is to test different theories of gravity. In this work we study gravitational lensing in the context of Palatini f(R) gravity using WKB approximation in the geometric optics limit and beyond. 
Monday, 16:1516:30 

Coffe Break 
Monday, 16:3016:55, A101 

Alexey Toporensky 
Multidimension cosmology in GaussBonnet gravity 
A successful compactification scenario should explain two, in principle, rather different properties of the multidimensional spacetime. First, we need to show why the evolution of three big dimension is different from the evolution of other dimensions. Second, we need to explain why the 3dimension subspace is almost isotropic one. We present a scenario which address both issures. Starting from rather general totally anisotropic initial condition the evolution of a Universe naturally leads to a product of two isotropic subspaces. This presentation is a brief summary of a set of papers made in collaboration with A.Giakomini, S.Pavluchenko and D. Chirkov. 
Monday, 16:3016:55, A102 

Mercè Guerrero Román 
Multiring images of regular compact objects 
We discuss the importance of multiring images in the optical appearance of spherically symmetric compact objects, when illuminated by an optically and geometrically thin accretion disk. On the one hand, we shall consider some spherically symmetric black hole and wormhole geometries characterized by the presence of a second critical curve, via a uniparametric family of extensions of the Schwarzschild metric. We will show the presence of additional light rings in the intermediate region between the two critical curves. On the other hand, a subcase of an analytically tractable extension of the Kerr solution, with both a critical curve and an infinite potential barrier at the object’s center for null geodesics. Our results point out to the existence of multiring images with a nonnegligible luminosity in shadow observations. 
Monday, 16:5517:20, A101 

Luiz Garcia de Andrade 
EinsteinCartanMaxwellHolst Gravity and Chiral Magnetic Dynamos 
We review the Einstein Cartan Holst gravity status and introduce the Holst current concept as an additional source for cosmological dynamo amplification 
Monday, 16:5517:20, A102 

Omar Valdivia 
Linear and Secondorder Geometry Perturbations on Spacetimes with Torsion 
In order to study gravitational waves in any realistic astrophysical scenario, one must consider geometry perturbations up to second order. Here, we present a general technique for studying linear and quadratic perturbations on a spacetime with torsion. Besides the standard metric mode, a “torsionon” perturbation mode appears. This torsional mode will be able to propagate only in a certain kind of theories. 
Monday, 18:1521:00 

Reception 
See Social Program 
Tuesday, 09:1510:15, A106 

Mikhail Shaposhnikov 
EinsteinCartan gravity: Inflation and Dark Matter 
It is wellknown since the works of Utiyama and Kibble that the gravitational force can be obtained by gauging the Lorentz group, which puts gravity on the same footing as the Standard Model fields. The resulting theory  EinsteinCartan gravity  happens to be very interesting. It may incorporate cosmological inflation driven by the Higgs field of the Standard Model of particle physics. In addition, it contains a fourfermion interaction that originates from torsion associated with spin degrees of freedom. This interaction leads to a novel universal mechanism for producing singlet fermions in the Early Universe. These fermions can play the role of dark matter particles. 
Tuesday, 10:1510:45 

Coffee Break / Poster Viewing 
Tuesday, 10:4511:45, A106 

Gonzalo J. Olmo 
Rotating solutions in RicciBased Gravity theories and the EiBI model 
Considering the EiBI gravity model, I will summarize how one can construct axisymmetric solutions in RicciBased Gravity theories (RBGs) using an algebraic correspondence between RBGs and General Relativity. If time permits, physical implications for the counterpart of the KerrNewman black hole coupled to Maxwell electrodynamics will be discussed. 
Tuesday, 11:4512:00 

Group Picture 
Tuesday, 12:0013:00 

Lunch 
Tuesday, 13:0013:25, A101 

Carlo Marzo 
Radiatively stable unitarity in higherspin models, and applications in metricaffine gravity 
The scrutiny of gravitational theories beyond EinsteinHilbert enjoys a different standard than flat models probed at colliderlevel energies. Of the proposed extensions, only a subset is explicitly required to be free of ghosts. Even in such cases, only dipole ghosts are usually targeted, thus still allowing, in general, wrongsign states to propagate. Moreover, even in rare cases where a thorough spectral analysis is performed, the stability of the resulting action under radiative corrections is uncertain. In this talk, I discuss the strong constraining power of requiring, as standard for lowerspin models, a radiatively stable ghost and tachyonfree action for the paradigmatic scenario of metricaffine gravity. I will describe the role of nonaccidental symmetries and their interplay with diffeomorphism invariance. I will also provide, in a more general way, an overview of the computational challenges on the way of the spectrum of higherspin theories. 
Tuesday, 13:0013:12, A102 

Sebastian Bahamonde 
Black holes in torsional teleparallel gravity 
The torsional teleparallel gravity is constructed from a manifold with torsion and zero curvature while respecting the metric compatibility condition. In this talk, I will discuss spherical symmetry in this formalism and present new exact black hole solutions for \(f(T,B)\) gravity and also scalarized solutions from scalartorsion theories of gravity. 
Tuesday, 13:1213:25, A102 

Christian Pfeifer 
Teleparallel accretion discs and gravitational waves 
In this talk I will present recent results on observables in teleparallel gravity:

Tuesday, 13:2513:50, A101 

Oleg Melichev 
MetricAffine Gravity as an Effective Field Theory 
We discuss theories of gravity with independent metric (or frame field) and connection, from the point of view of effective field theory. In general, in addition to the metric, gravitational interactions can be carried by torsion field, or nonmetricity, or both. This theory reduces to the General Relativity at low energies in the natural scenario, but enjoys nontrivial dynamics at high energies as long as dimension four operators, such as curvature squared, are considered. We count such operators of even parity and give explicit bases for the independent ones that contribute to the twopoint function. We then give the decomposition of the linearized action on a complete basis of spin projectors and consider various subclasses of MetricAffine Gravity (MAG) theories. We proceed with discussion of ghost and tachyonic instabilities and construct simple MAGs that contain only a massless graviton and a state of spin/parity 2 or 3 and therefore are stable. Finally, we discuss the renormalisation group flow of the theory. 
Tuesday, 13:2513:50, A102 

Muzaffer Adak 
Weyl covariance, second clock effect and proper time in theories of symmetric teleparallel gravity 
We give a new prescription of parallel transport of a vector tangent to a curve which is invariant under both of a local general coordinate and a Weyl transformation. Thus, since the length of tangent vector does not change during parallel transport along a closed curve in spacetimes with nonmetricity, a second clock effect does not appear in general, not only for the inetgrable Weyl spacetime. We have specially motivated the problem from the point of view of symmetric teleparallel (or MinkowskiWeyl) geometry. We also conclude that as long as nature respects Lorentz symmetry and Weyl symmetry, one can only develop alternative gravity models in the symmetric teleparallel spacetime (Q≠0,T=0,R=0) or the most general nonRiemannian spacetime (Q≠0,T≠0,R≠0). 
Tuesday, 13:5014:15, A101 

Hardi Veermäe 
Preheating in Palatini R^2 gravity 
In the Palatini formalism with an R^2 term, inflation potentials will be flattened to form a plateau in the Einstein frame. In such models, the inflaton field can repeatedly return to this plateau after inflation. This results in an active tachyonic instability which effectively fragments the inflaton condensate in less than an efold. We will discuss tachyonic preheating in Palatini R^2 gravity and in the family of plateau models in general. 
Tuesday, 13:5014:15, A102 

Philip Schwartz 
Teleparallel Newton–Cartan gravity 
We discuss a teleparallel version of Newton–Cartan gravity. This theory arises as a formal largespeedoflight limit of the teleparallel equivalent of general relativity (TEGR). Thus, it provides a geometric (‘covariant’) formulation of the Newtonian limit of TEGR, analogous to standard Newton–Cartan gravity being the geometric formulation of the Newtonian limit of general relativity. We show how by a certain gaugefixing the standard formulation of Newtonian gravity can be recovered. 
Tuesday, 14:1514:40, A101 

Alexandros Karam 
Palatini Inflation 
We present various aspects of modified gravity inflationary scenarios when studied in the Palatini formalism. 
Tuesday, 14:1514:40, A102 

Fidel Fernández Villaseñor 
Metricaffine Finslerian gravity 
Over the last years, there has been an increasing interest and amount of results in alternative theories of gravitation based on (Lorentz)Finsler geometry. An important achievement has been an equation obtainable by applying the metric variation to a geometric functional [1,2]. In this presentation, based upon [3], we apply the Palatini formalism to the same Finslerian action. We also clarify the structure of the solutions with torsion, extending the classical case [4]. Then, assuming certain regularity at the lightlike directions, we obtain results which provide: A) The uniqueness of the torsionfree (nonlinear) connection, and B) The equivalence of the vacuum equation with the vanishing of the Finslerian Ricci scalar of such connection. References: [1] C. Pfeifer and M. R. Wohlfart: Finsler geometric extension of Einstein gravity. Phys. Rev. D (Vol.85, No.6), 2012. [2] M. Hohmann, C. Pfeifer and N. Voicu: Finsler gravity action from variational completion. Phys. Rev. D 100, 064035 (2019). [3] M. Á. Javaloyes, M. Sánchez and F. F. Villaseñor: The EinsteinHilbertPalatini formalism in pseudoFinsler geometry. ArXiv eprints, arXiv:2108.03197v2 [math.DG] (2021). [4] A. N. Bernal et al.: On the (non)uniqueness of the LeviCivita solution in the EinsteinHilbertPalatini formalism. Phys.Lett. B768 (2017) 280287. 
Tuesday, 14:4015:00 

Coffe Break 
Tuesday, 15:0015:25, A101 

Margus Saal 
The slowroll approximation: accurate enough to estimate different models of inflation? 
The spectral index of scalar perturbation n and the ratio of tensortoscalar perturbation r are often used to estimate the consistency of inflation models with the observed results. Extending the theory of gravity to the scalartensor type theory, we show in the presentation how very different models can give the same values for n and r. This suggests that these quantities may not be sufficient to determine whether or not the model is consistent with the observations. We analyze this problem and offer solutions for what and how the model should be further evaluated. 
Tuesday, 15:0015:25, A102 

Yakov Itin 
Energymomentum tensor: Noether vs Hilbert. 
In this paper, the relationship between two basic definitions of the energymomentum tensor in field theory is discussed. Hilbert’s definition is based on the variation derivative of the Lagrangian with respect to the metric tensor. By definition, the resulting tensor is symmetric. The conservation of this tensor, on the other hand, requires the use of field equations. Noether’s definition is based on the symmetry of the Lagrangian with respect to the diffeomorphism invariance. This tensor is not symmetric, but it can be symmetrized with the use of the BelinfanteRosenfeld procedure. The conservation of this tensor is selfevident from its definition. Noether’s tensor vanishes on shell modulo a divergence of an arbitrary superpotential. For most essential applications, such as YangMills models, two tensors become equal despite having extremely different features. Moreover, they provide meaningful (and measurable) conserved quantities. In this study, we show that in some natural field models the tensors are actually equivalent. Our analysis is based on a teleparallel spacetime and differentialform representation. We examine the examples of the free pform gauge field theory, the GR in the coframe representation, and the metricfree electrodynamics. 
Tuesday, 15:2515:50, A101 

Christian Dioguardi 
Slowroll inflation in Palatini F(R) gravity 
We study single field slowroll inflation in the presence of \(F(R)\) gravity in the Palatini formulation. In contrast to metric \(F(R)\), when rewritten in terms of an auxiliary field and moved to the Einstein frame, Palatini \(F(R)\) does not develop a new dynamical degree of freedom. However, it is not possible to solve analytically the constraint equation of the auxiliary field for a general \(F(R)\). We propose a method that allows us to circumvent this issue and compute the inflationary observables. We apply this method to test scenarios of the form \(F(R)=R+αR^n\) and find that, as in the previously known \(n=2\) case, a large \(α\) suppresses the tensortoscalar ratio \(r\). We also find that models with \(F(R)\) increasing faster than \(R^2\) for large \(R\) suffer from numerous problems, with possible implications on the theoretically allowed UV behaviour of such Palatini models. 
Tuesday, 15:2515:50, A102 

Elena Emtsova 
On conservation laws in STEGR 
We derive conservation laws in STEGR with direct application of Noether’s theorem. This approach allows to construct covariant conserved currents, corresponding superpotentials and invariant charges. By calculating currents, one can obtain local characteristics of gravitational field like energy density. Surface integration of superpotentials gives charges which correspond to global quantities of the system like mass, momentum, etc. To test our results for the obtained currents and superpotentials, we calculate the energy density measured by freely falling observer in the simple solutions (Schwartzchild black hole, FRLW) and total mass of the Schwartzchild black hole. We find ambiguities in obtaining the connection, which explicitly affect the values of conserved quantities, and discuss a constructive solution to this problem. 
Tuesday, 15:5016:15, A101 

Haidar Sheikhahmadi 
Inflation in Hybrid Metric Palatini Gravity 
We consider an inflationary scenario in the framework of the Hybrid Metric Palatini Gravity in which a supplementary term, containing a Palatini type correction is added to the standard GR action. This configuration can be reformulated into the equivalent form of a scalartensor theory, in which a low mass scalar field can explain the observed gravitational phenomenology, by generating longrange forces that pass all the local tests without invoking any kind of screening mechanism, chameleon scenario for instance. We look over the possibility that this effective scalar field may generate the matter content of the early Universe. 
Tuesday, 15:5016:15, A102 

Débora Aguiar Gomes 
Energy and entropy in the Geometrical Trinity of gravity 
All energy is gravitational energy. That is the consequence of the equivalence principle, according to which gravity is the universal interaction. The physical charges of this interaction have remained undisclosed, but the Advent of the Geometrical Trinity opened a new approach to this foundational problem. Here it is shown to provide a backgroundindependent unification of the previous, noncovariant approaches of BergmannThomson, Cooperstock, Einstein, von Freud, LandauLifshitz, Papapetrou and Weinberg. First, the Noether currents are derived for a generic Palatini theory of gravity coupled with generic matter fields, and then the canonical i.e. the unique charges are robustly derived and analysed, particularly in the metric teleparallel and the symmetric teleparallel versions of General Relativity. These results, and their application to black holes and gravitational waves, are new. 
Tuesday, 16:1516:30 

Coffe Break 
Tuesday, 16:3017:20 

Discussion (MetricAffine Gravity: geometry vs matter interpretation) 
Discussion leader: Adrià Delhom I Latorre 
Tuesday, 18:1519:15 

Public Talk  Rodrigues 
Prof. Davi Rodrigues will speak at the historic Tartu Old Observatory on the topic “Why do galaxies rotate?” 
Wednesday, 09:1510:15, A106 

Branislav Cvetkovic 
Hamiltonian approach to entropy in Poincare gauge theory 
The canonical generator \(G\) of local symmetries in Poincare gauge theory is constructed as an integral over a spatial section \(\Sigma\) of spacetime. Its regularity (differentiability) on the phase space is ensured by adding a suitable surface term, an integral over the boundary of at infinity, which represents the asymptotic canonical charge. For black hole solutions, \(\Sigma\) has two boundaries, one at infinity and the other at horizon. It is shown that the canonical charge at horizon defines entropy, whereas the regularity of G implies the first law of black hole thermodynamics. The approach is tested for several black hole types. 
Wednesday, 10:1510:30 

Coffee Break / Poster Viewing 
Wednesday, 10:3011:00, A106 

Tomi Koivisto 
ΛCDM theory of cosmology 
The constants Λ and the CDM in the standard model of cosmology arise as integration constants in the derivation of Einstein’s equations from the gauge theory of the Lorentz group. 
Wednesday, 11:0011:25, A106 

Emanuele Orazi 
Conformal Invariant MetricAffine Gravity Theories 
A recent revival of the link between conformal symmetry and projective invariance in the framework of metricaffine gravity theories motivated a systematic study of a general strategy to build a conformal version of any modified gravity. In this oral presentation will be clarified the underlying gauge symmetry associated to conformal invariance and its theoretical and phenomenological implications deriving from the explicit solutions of field equations in the metric affine formalism. 
Wednesday, 11:2511:50, A106 

Yuri Bonder 
Symmetries in gauge theories of gravity with and without nondynamical fields 
I will present a transparent and concise method to write generic gauge theory, including gravity gauge theories, and extract the corresponding symmetries from the Lagrangian equations of motion. This method can be applied to theories where the symmetries are broken by the presence of nondynamical fields. As an example, I will discuss unimodular gravity in the first order formalism, where invariance under diffeomorphisms is partially broken. Still, the method can be used to read off the remaining symmetries. Remarkably, the symmetry algebra was calculated and it is possible to verify that it is has the expected properties. 
Wednesday, 11:5012:15, A106 

Gerardo GarcíaMoreno 
On the differences between General Relativity and Unimodular Gravity 
Weyl TransverseDiffeomorphisms (WTDiff) gravity is a theory so closely related to General Relativity (GR) that one can wonder to what extent they are really different. Unimodular gravity can be thought as a simple gauge fixing of WTDiff and hence completely equivalent to it. WTDiff and GR are based on two different gauge symmetries: WTDiff is based on Transverse Diffeomorphisms and Weylrescalings of an auxiliary metric, whereas GR is based on the full group of diffeomorphisms. The formal difference appears due to the existence of a fiduciary background structure, a fixed volume form, in WTDiff theories. In this talk I will present an overview as complete as possible of all the situations and regimes in which one might suspect that some differences between these two theories might arise. This overview contains analysis in the classical, semiclassical and quantum regimes. 
Wednesday, 12:1513:30 

Lunch 
Wednesday, 13:3021:30 

Excursion 
See Social Program 
Thursday, 09:1510:15, A106 

Jose Beltran Jimenez 
The harzards in Affinesia: Quicksands and sweet spots 
The equivalence principle naturally provides gravity with a geometrical character, thus making the metricaffine framework be a natural land for gravity theories. However, the precise geometry we employ admits a certain flexibility and, in particular, Einstein’s gravity can be equivalently ascribed to the three independent objects that characterise a connection, i.e., curvature, torsion and nonmetricity. After reviewing these three alternative descriptions of gravity, I will uncover how pathologies generally arise beyond these GR equivalents and illustrate with some examples how to get around them. 
Thursday, 10:1510:45 

Coffee Break / Poster Viewing 
Thursday, 10:4511:10, A106 

Manuel Hohmann 
General cosmologies and their perturbations in teleparallel gravity 
Within the framework of teleparallel gravity, a flat affine connection is used as a dynamical field in addition to the metric tensor. Depending on the class of theories, this connection may further be restricted by imposing either vanishing torsion or vanishing nonmetricity. In the field of cosmology, most commonly a particular, simple, homogeneous and isotropic connection has been chosen, and its background dynamics and perturbations have been studied for different theories. While this does lead to a set of cosmological dynamical equations, it is far from being the most general cosmological dynamics in teleparallel gravity. This presentation gives a complete classification of all homogeneous and isotropic teleparallel geometries (general, metric and symmetric), as well as their perturbations. For the latter, gauge transformations and gauge invariant quantities are presented. It is shown that:
and that the two latter cases arise as limits of the first. 
Thursday, 11:1011:35, A106 

Jackson Said 
Traditional and Novel approaches to model selection in f(T) gravity using recent observational cosmology 
Teleparallel gravity offers numerous possible classes of theories and arbitrary models in each class. One such example is f(T) gravity where any functional form of the torsion scalar is included. The problem of reducing the space of viable functions has led to several recent interesting avenues of research. Traditionally, models in theories like f(T) gravity would be chosen to meet specific observational or theoretical conditions, which would then be constrained against various observations using Bayesian methods. Recent works in the literature have proposed the use of machine learning techniques to reverse the way models are selected in theories like f(T) gravity so that observational data can be used to define the functional form of the model. In this talk, I will cover some of these new approaches and discuss how they compare with previous methods. 
Thursday, 11:3512:00, A106 

Alexey Golovnev 
Transferring the troubles from torsion to nonmetricity 
It is a very interesting field of modified gravity research now, constructing modifications starting from alternative geometrical foundations. It gives very exciting new angles to look at general relativity, in particular because no simple modifications of this sort appear to be healthy. I will briefly review the foundational issues of modified teleparallel gravity, then discuss modified symmetric teleparallel models, and compare the two approaches. 
Thursday, 12:0013:00 

Lunch 
Thursday, 13:0013:25, A101 

Daniel Blixt 
Lorentz symmetries in teleparallel theories of gravity 
Teleparallel gravity is a peculiar limit in the metric affine frameworks of gravity where curvature is taken to zero and still a classically equivalent to general relativity can be found. In its original formulation teleparallel gravity breaks Lorentz invariance at minimum at the boundary and in its most generic case fully. Later there was a realization that a spin connection can be introduced for which Lorentz transformations of the couple tetrad and spin connection leaves the action invariant. This is referred to as the covariant formulation of teleparallel gravity. In this talk I will give deeper insights of Lorentz symmetries in teleparallel theories of gravity referring to both a simple observation as well as to the Hamiltonian analysis and highlight the relation to physical degrees of freedom. 
Thursday, 13:0013:25, A102 

Bivudutta Mishra 
Reconstruction of Matter Bounce Cosmology in symmetric teleparallel gravity 
In this paper, we have constructed the cosmological model of the universe that shows the bouncing scenario. We have obtained specific form of the function f(Q) that shows the bouncing behavior at the backdrop of homogeneous and isotropic spacetime, Q being the nonmetricity. The dynamics of the model has been studied with the help of critical points and the stability behavior has been discussed. 
Thursday, 13:2513:50, A101 

MariaJose Guzman 
Canonical structure of symmetric teleparallel and f(Q) gravity 
Modified gravities based on nonmetricity of spacetime have gained an increased attention in recent years. In particular, f(Q) gravity models come as the simplest generalization of the symmetric teleparallel equivalent of general relativity, and are intensively used in cosmological applications. However, the question of the number of physical degrees of freedom and their behavior is not clear. In this talk we will review the literature and recent progress on the Hamiltonian formalism for symmetric teleparallel and f(Q) gravity, compare to the controversial case of f(T) gravity, and derive conclusions that might be of help for future research. 
Thursday, 13:2513:50, A102 

Laxmipriya Pati 
Rip cosmological models in extended symmetric teleparallel gravity 
In this work, we have investigated some rip cosmological models in an extended symmetric teleparallel gravity theory. We consider the form f(Q, T) = aQ^m+bT in the Einstein–Hilbert action and expressed the field equations and the dynamical parameters in terms of the nonmetricity ‘Q’. Three rip models such as Little Rip, Big Rip and Pseudo Rip are presented. The energy conditions and the cosmographic parameters are derived and analysed for all these models. 
Thursday, 13:5014:15, A101 

Franco Fiorini 
Remnant symmetries in f(T)like models: lessons from 2D 
By constructing twodimensional, nonlocal Lorentz invariant gravitational actions based on the torsion tensor, we discuss the physical meaning of the remnant symmetries associated with the nearhorizon geometry experienced by a radial observer in Schwarzschild spacetime. These symmetries, which represent special or privileged diads, acquire the form of uniformly accelerated (Rindler) observers whose constant acceleration is proportional to the black hole mass M. 
Thursday, 13:5014:15, A102 

Simran Arora 
Constraining effective equation of state in f (Q, T) gravity 
New highprecision observations are now possible to constrain different gravity theories. To examine the accelerated expansion of the Universe, we used the newly proposed f(Q,T) gravity, where Q is the nonmetricity, and T is the trace of the energymomentum tensor. The investigation is carried out using a parameterized effective equation of state with two parameters, m and n. We have also considered the linear form of f(Q,T) = Q + b T, where b is constant. By constraining the model with the recently published 1048 Pantheon sample, we were able to find the best fitting values for the parameters b, m, and n. The model appears to be in good agreement with the observations. Finally, we analyzed the behavior of the deceleration parameter and equation of state parameter. The results support the feasibility of f(Q,T) as a promising theory of gravity, illuminating a new direction towards explaining the Universe’s dark sector. 
Thursday, 14:1514:40, A101 

Morgan Le Delliou 
Teleparallel Gravities as a gauge theories: TEGR and STGR, a work in progress 
Initiated with a question on the mathematical nature of the connection in the socalled “translations gauge theory” formulation of Teleparallel Equivalent to General Relativity (TEGR) Theory, our explorations led us to consider a novel approach using a Cartan connection. The mathematically admitted underlying structure of a gauge theory for a symmetry group \(G\) relies on a principal \(G\)bundle on which is chosen a connection (the gauge field). The bundle formalism with connection allows to distinguish in the structure of TEGR as “translations gauge theory” that the algebra of translations is indeed necessary to build the torsion, which could resemble the field strength of that gravity. However, the corresponding field clearly does not present the structure of a connection. Nevertheless, the translation field can be integrated in a Cartan connection, as shown in our approach, which allows to keep the interpretation of the translation field as related to a connection. The coupling to matter can be performed thanks to a Cartan connection and a theorem by Sharpe to obtain a consistent and complete description of TEGR that confirms its difference with the usual structures of gauge theories. The approach to STGR involves a closer examination of bundle reduction and soldering form that appear to mark the specificity of gravity. Although the frame field remains the best candidate for what could be recognised as a gauge field, the introduction of a distinct soldering form through a bundle reduction giving birth to the metric on the base leads to a specific structure. To bring such a framework closer to a theory with a connection will require more investigations. 
Thursday, 14:1514:40, A102 

Siddheshwar Kadam 
Dynamical features of \(f(T,B)\) cosmology 
In this paper, we have explored the field equations of \(f(T, B)\) gravity and determined the dynamical parameters with the hyperbolic function of the Hubble parameter. The accelerating behavior has been observed and the behavior of the equation of state parameter indicates the \(\Lambda CDM\) model at a late time. The role of model parameters in assessing accelerating behavior has been emphasized. The stability of the model is analyzed by using scalar perturbation. 
Thursday, 14:4015:00 

Coffe Break 
Thursday, 15:0015:25, A101 

Ludovic Ducobu 
Scalarized Black Holes in Teleparallel Gravity 
If General Relativity [GR] offers an extremely successful framework to describe the gravitational interaction, whose achievements range from the solar system to the cosmological scale, the necessity to question the framework of GR is clear at both the experimental and theoretical levels. Since not all of the current puzzles can be purely reduced to quantum correction problems, this motivates the study of alternative theories of gravitation already at the classical level. Among the many possible directions one can follow, an interesting one consists in the addition of new degrees of freedom in the theory (in addition to the spacetime metric). In this respect, the simplest candidate is a scalar field. Alternative theories of gravity including a scalar field have attracted a lot of attention in the past decade. This is especially true for Horndeski gravity; the most general scalartensor theory of gravity in 4D, based on the same geometrical framework as GR, including a real scalar field and presenting second order field equations. The aim of this talk will be to introduce recent results of our research in the context of teleparallel theories of gravity extended by scalar fields. I will start by a short synopsis of the main features of teleparallel theories of gravity compared to metric based theories (especially GR). I will then discuss recent results regarding hairy black holes for some teleparallel theories of gravity endowed with a nonminimally coupled real scalar field. If time permits, I will comment on how one could possibly extend results obtained for metric based scalartensor theories of gravity using the framework of teleparallel gravity. 
Thursday, 15:0015:25, A102 

Armando Aram Reyes Aguilar 
Inhomogeneous solutions in \(f(T,B)\) gravity 
In this paper, we explore the possibility to find exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric LemaîtreTolmanBondi (LTB) dust models. We apply to the LTB metric the formalism of TG in its extension to \(f(T,B)\) models, which can be seen as the analogous from the Schwarzschild solution in General Relativity. An exact LTB solution is obtained which is compatible with a specific \(f(T,B)\) model whose observational constraints are cosmologically viable in a standard spatially flat RobertsonWalker geometry. 
Thursday, 15:2515:45, A101 

Joosep Lember 
Black hole solutions in scalartensor symmetric teleparallel gravity 
Symmetric teleparallel gravity is constructed with a nonzero nonmetricity tensor while both torsion and curvature are vanishing. In this framework, we find exact scalarised spherically symmetric static solutions in scalartensor theories built with a nonminimal coupling between the nonmetricity scalar and a scalar field. It turns out that the BocharovaBronnikovMelnikovBekenstein solution has a symmetric teleparallel analogue (in addition to the recently found metric teleparallel analogue), while some other of these solutions describe scalarised black hole configurations that are not known in the Riemannian or metric teleparallel scalartensor case. To aid the analysis we also derive nohair theorems for the theory. Since the symmetric teleparallel scalartensor models also include \(f(Q)\) gravity, we shortly discuss this case and further prove a theorem which says that by imposing that the metric functions are the reciprocal of each other (\(g_{rr}=1/g_{tt}\)), the \(f(Q)\) gravity theory reduces to the symmetric teleparallel equivalent of general relativity (plus a cosmological constant), and the metric takes the (Anti)deSitterSchwarzschild form. 
Thursday, 15:2515:45, A102 

Paul Martin Kull 
Nonexotic wormholes in \(f(R,T)\) gravity 
In this work, stable traversable wormhole models that satisfy at least the null energy condition (NEC) everywhere are developed in the geometric representation of \(f(R,T)\) gravity. The NEC is satisfied both everywhere in the wormhole spacetime and by using the thinshell formalism to match the wormhole spacetime with an exterior vacuum spacetime. In the first case, conditions are determined for the particular forms of the shape and redshift functions \(b(r)\) and \(\zeta(r)\) considered that guarantee that the resulting spacetime satisfies at least the NEC everywhere. In the second case, after deriving the junction conditions for the particular form of the theory used, one finds that the radius \(r_\Sigma\) of the thinshell is not restricted to single values for some values of the throat radius \(r_0\). This allows one to choose \(r_\Sigma\) and \(r_0\) such that the weak energy condition can also be satisfied everywhere. 
Thursday, 15:4516:10, A101 

Laur Järv 
Spherically symmetric static spacetime in the coincident gauge of symmetric teleparallel gravity 
In the context of symmetric teleparallel gravity the coincident gauge denotes a coordinate system where the affine connection vanishes globally and the covariant derivatives reduce to partial derivatives. Despite the allure for computational ease, explicit examples of this are hard to come by. In the talk we consider general metric and affine connection which both are spherically symmetric and static, and transform this configuration into the coincident gauge. We conclude with a comparison to the Weitzenböck gauge in metric teleparallelism, and remarks about the notion of ‘purely inertial connection’. 
Thursday, 15:4516:10, A102 

Vesselin Gueorguiev 
Main Results and Current Progress within the Scale Invariant Vacuum Paradigm 
A review of the Scale Invariant Vacuum (SIV) idea will be presented as related to Weyl Integrable Geometry [1]. The main results related to SIV and inflation [2], the growth of the density fluctuations [3], and the application of the SIV to scaleinvariant dynamics of Galaxies, MOND, Dark Matter, and the Dwarf Spheroidals [4] will be highlighted. [1] Gueorguiev, V. G., Maeder, A., The Scale Invariant Vacuum Paradigm: Main Results and Current Progress. Universe 2022, 8 (4) 213; DOI:10.3390/universe8040213 [grqc/2202.08412]. [2] Maeder, A., Gueorguiev, V. G., Scale invariance, horizons, and inflation. MNRAS 504, 4005 (2021) [grqc/2104.09314]. [3] Maeder, A., Gueorguiev, V., G., The growth of the density fluctuations in the scaleinvariant vacuum theory. Phys. Dark Univ. 25, 100315 (2019) [astroph.CO/1811.03495] [4] Maeder, A.; Gueorguiev, V.G. Scaleinvariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals. MNRAS 492, 2698 (2019) [grqc/2001.04978] 
Thursday, 16:1016:25 

Coffe Break 
Thursday, 16:2517:20 

Discussion (Teleparallel Gravity: viable or not) 
Discussion leader: Christian Pfeifer 
Thursday, 19:0021:00 

Conference dinner 
See Social Program 
Friday, 09:1509:45, A106 

Davi Rodrigues 
Testing modified gravity rotation curves with the Normalized Additional Velocity method 
I will introduce the Normalized Additional Velocity (NAV) method and show how to apply it, with focus on modified gravity (although it can also be useful for dark matter profiles). The method will be illustrated with several models, including \(f(R)\) Palatini, EddingtoninspiredBornInfeld (EiBI), MOND and others. It is a complementary and fast approach to study galaxy rotation curves (RCs) directly from the sample distribution, instead of first performing several individual RC fits. It does not cover all the RC properties, but it focuses on the shape of the nonNewtonian contribution for a given sample (we use 122 SPARC galaxies). A relevant advantage, when applying the method to modified gravity models, is that for several models it is possible to use approximations that circumvent the need for solving modified Poisson equations for each one of the galaxies. Among other results, we show that \(f(R)\) Palatini and EiBI gravities cannot be used to replace dark matter in galaxies, while MOND has reasonable results, although with an issue. Based on https://arxiv.org/abs/2204.03762 and more recent developments. 
Friday, 09:4510:15, A106 

Emmanuel Saridakis 
Tracing torsional gravity in the early universe: primordial black holes and gravitational waves 
There is a huge variety of gravitational modifications constructed for theoretical reasons, namely to alleviate the renormalizability issues of General Relativity, as well as for cosmological reasons, namely to successfully describe the Universe evolution and alleviate possible observational tensions. It is time to start using the rich observational datasets of increasing accuracy in order to distinguish between them. We search for signatures and smoking guns of torsional modified gravity in late and earlytime cosmological observations, focusing on gravitational waves and primordial black holes. 
Friday, 10:1510:20 

Closing remarks 
We end the last parallel session with a few comments on previous and possible future meetings. 
Friday, 10:2010:45 

Coffee Break / Poster Viewing 
Friday, 10:4511:10, A101 

Orest Hrycyna 
A new generic and structurally stable cosmological model without singularity 
Dynamical systems methods are used to investigate a cosmological model with nonminimally coupled scalar field and asymptotically quadratic potential function. We found that for values of the nonminimal coupling constant parameter \(\frac{3}{16}\lt\xi\lt\frac{1}{4}\) there exists an unstable asymptotic de Sitter state giving rise to nonsingular beginning of universe. The energy density associated with this state depends on value of the nonminimal coupling constant and can be much smaller than the Planck energy density. For \(\xi=\frac{1}{4}\) we found that the initial state is in form of the static Einstein universe. Proposed evolutional model, contrary to the seminal Starobinsky’s model, do not depend on the specific choice of initial conditions in phase space, moreover, a small change in the model parameters do not change the evolution thus the model is generic and structurally stable. The values of the nonminimal coupling constant can indicate for a new fundamental symmetry in the gravitational theory. We show that Jordan frame and Einstein frame formulation of the theory are physically nonequivalent. 
Friday, 10:4511:10, A102 

Monika E. Pietrzyk 
Covariant HamiltonJacobi Equation for the Teleparallel Equivalent of General Relativity 
The covariant De DonderWeyl Hamiltonian theory of the Teleparallel Equivalent of General Relativity is formulated using the methods developed by I. Kanatchikov within his approach of precanonical quantization. Based on the results from the geometric HamiltonJacobi theory for variational problems we derive a covariant HamiltonJacobi equation for TEGR which generalizes the covariant HamiltonJacobi equation for General Relativity which was obtained by Th. De Donder (1930) and P. Hoava (1991). I also comment on the problem of the relation between the canonical HJ equations derived from the canonical ADM formalism and the covariant HJ equations derived from the De DonderWeyl Hamiltonian theory. The covariant HJ equation can be used for numerical simulations or as a test of the classical limit of quantum TEGR, its quasiclassical study and Bohmianlike formulation. Based on my joint paper with C. Barbachoux: ePrint: 2201.01295 [grqc]. 
Friday, 11:1011:35, A101 

Nurgissa Myrzakulov 
Symmetric teleparallel f(Q) gravity with nonminimally coupled fermion field 
In this work, we explore the symmetric teleparallel \(f(Q)\) gravity, which is nonminimally coupled with the fermion field in the FriedmannRobertsonWalker metric. By using the Lagrange multiplier modified Friedmann equations, Dirac equations for the fermion field are obtained. Using the Noether symmetry method, the form of the coupling between gravity and matter, the selfconsistent potential, the symmetry generators, the form of \(f(Q)\) gravity, and the conserved quantity for this model are determined. Cosmological solutions describe the latetime accelerated expansion of the Universe obtained. 
Friday, 11:1011:35, A102 

Igor Kanatchikov 
Towards quantum geometric trinity of gravity 
We plan to present (i) a reformulation of the classical geometric trinity of gravity which allows discussing quantization of equivalent descriptions of general relativity within a unifying framework, (ii) the covariant Hamiltonian formulation of the trinity based on the polysymplectic formalism and the PoissonGerstenhaber brackets of differential forms, and the Diraclike analysis of constraints, (iii) a quantum formulation of the trinity based on the quantization of the analog of Dirac brackets in the above formalism that leads to three different covariant generalizations of the Schroedinger (or WheelerDewitt) equation for quantum gravity. They treat spacetime dimensions on equal footing and describe quantum geometry in terms of Cliffordalgebravalued amplitudes of spinconnection (in GR) or vielbeins (in TEGR), or metric density (in Coincident GR). We briefly discuss a relation to the canonical ADM formulations and the canonical quantization, the emergence of the classical limit, the nonGaussian statistics of quantum gravitational fluctuations in a cosmological context, a naive estimation of the quantum gravity contribution to the cosmological constant, and the scale when quantumgravitational fluctuations “foam” classical spacetime, which turns out to be significantly subPlanckian. 
Friday, 11:3512:00, A101 

Santosh Lohakare 
Cosmological model with time varying deceleration parameter in F(R, G) gravity 
In this work, we investigate the dynamical behavior of the Universe in the F(R, G) theory of gravity, where R and G indicate the Ricci scalar and GaussBonnet invariant, respectively. The energy conditions, cosmographic parameters, stability, and the possibility of recreating the mentioned model using a scalar field formalism are all part of our comprehensive research. At late times, the model obtained here exhibits quintessencelike behavior. 
Friday, 11:3512:00, A102 

Abdel Nasser Tawfik 
On possible quantization of metric tensor and affine connection 
When the minimal length approach emerging from noncommutative Heisenberg algebra, generalized uncertainty principle, and thereby integrating gravitational fields to this fundamental theory of quantum mechanics (QM) is thoughtfully extended to general relativity (GR), the possible quantization of the fundamental tensor is suggested. This is a complementary term reconciling principles of QM and GR and comprising noncommutative algebra together with maximal spacelike fouracceleration. That quantization compiles with GR as curvature in relativistic eightdimensional spacetime tangent bundle, Finsler spacetime, the generalization of the pseudoRiemannian spacetime, is the recipe applied to derive the quantized metric tensor. This dictates how the affine connection on pseudoRiemannian manifold is straightforwardly quantized. We have discussed the symmetric property of quantized metric tensor and affine connection. 
Friday, 12:0012:25, A101 

Amarkumar Agrawal 
Matter bounce scenario in the functional form of f(R) gravity 
We examined bouncing cosmological models in an isotropic and homogeneous spacetime with the f(R) theory of gravity. The bouncing scale factor was used to study two functional forms of f(R). Along with the cosmographic parameters, the dynamical parameters are calculated and analysed. Both the models’ analyses reveal the presence of bounce. In both models, the violation of strong energy conditions is also shown. 
Friday, 12:0012:25, A102 

Sravan Kumar 
Probing quantum gravity and nonlocality through R^2like inflation 
Cosmic inflation is an important paradigm of the early Universe which is so far developed in two equivalent ways, either by geometrical modification of Einstein’s general relativity (GR) or by introducing new forms of matter beyond the standard model of particle physics. Starobinsky’s R+R^2 inflation based on a geometric modification of GR is one of the most observationally favorable models of cosmic inflation based on a geometric modification of GR. In this talk, I will discuss in detail the fundamental motivations for Starobinsky inflation and present how certain logical steps in the view of its UV completion lead to the emergence of a gravity theory that is nonlocal in nature. Then I will establish how one can perform studies of the early Universe in the context of nonlocal gravity and what are the observational consequences in the scope of future CMB and gravitational waves. I will discuss in detail how nonlocal R^2like inflation can be observationally distinguishable from the local effective field theories of inflation. Finally, I will comment on the prospects of nonlocal gravity as a promising candidate for quantum gravity. 
Friday, 12:2512:45, A101 

Kärt Soieva 
The cooling process of brown dwarfs in Horndeski theory of gravity 
In the presentation the cooling process of brown dwarf stars in the framework of DHOST theories will be discussed. The analytical model and its numerical solutions are showcased. 
📅09:1510:15, A106
💻︎ Christian Boehmer (University College London, London, United Kingdom):
Modified theories of gravity  foundations and models
In the first part of the talk I am discussing General Relativity, in particular its basic ingredients and its mathematical structure. This will naturally lead the way to consider various modifications or extensions of General Relativity, many of which have been studied recently. Next I will discuss modified gravity models based on generalised geometries and on actions no longer linear in curvature. The main part of the talk will discuss how these many different theories can be studied using a single unified approach which also shows the equivalence of some of these models. Boundary terms in the action will play a crucial role in establishing the equivalence between different theories. The final part discusses the study of cosmological models using dynamical systems techniques.
📅10:4511:45, A106
👤︎ Francisco Lobo (Institute of Astrophysics and Space Sciences, University of Lisbon, Lisbon, Portugal):
Beyond Einstein’s General Relativity: Hybrid metricPalatini gravity and curvaturematter couplings
Einstein’s General Relativity (GR) is possibly one of the greatest intellectual achievements ever conceived by the human mind. In fact, over the last century, GR has proven to be an extremely successful theory, with a wellestablished experimental footing. However, the discovery of the latetime cosmic acceleration, which represents a new imbalance in the governing gravitational field equations, has forced theorists and experimentalists to question whether GR is the correct relativistic theory of gravitation, and has spurred much research in modified gravity, where extensions of the HilbertEinstein action describe the gravitational field. In this talk, I perform a detailed theoretical and phenomenological analysis of two largely explored extensions of f(R) gravity, namely: (i) the hybrid metricPalatini theory; (ii) and modified gravity with curvaturematter couplings. Relative to the former, it has been established that both metric and Palatini versions of f(R) gravity possess interesting features but also manifest severe drawbacks. A hybrid combination, containing elements from both formalisms, turns out to be very successful in accounting for the observed phenomenology and avoids some drawbacks of the original approaches. Relative to the curvaturematter coupling theories, these offer interesting extensions of f(R) gravity, where the explicit nonminimal couplings between an arbitrary function of the scalar curvature R and the Lagrangian density of matter, induces a nonvanishing covariant derivative of the energymomentum tensor. I explore both theories in a plethora of applications, namely, the weakfield limit, cosmology, and irreversible matter creation processes of a specific curvaturematter coupling theory.
📅13:0013:25, A101
👤︎ Adrià Delhom I Latorre (University of Tartu, Tartu, Estonia):
Identification of some redundant operators and a generalized Einstein frame in MAG theories
Inspired by recent findings involving RicciBased Theories, in this talk I will argue why, for theories reproducing GR at low energies which admit a perturbative expansion for the higher order corrections, and for which derivatives of the metric do not appear in the Lagrangian, the terms containing \(R^{\Gamma}_{(\mu\nu)}\) beyond the EinsteinHilbert term can be understood as redundant operators (in the Effective Field Theory sense) that can be reabsorbed into the interactions of the matter sector. At the same time, the form of the field equations suggests that the metric which describes gravitational perturbations is not the one in the original frame of the theory, namely \(g^{\mu\nu}\), but rather an object \(q^{\mu\nu}\) defined from the derivatives of the Lagrangian with respect to \(R^{\Gamma}_{(\mu\nu)}\). I will then try to outline the construction of a sort of generalized Einstein frame where \(q^{\mu\nu}\) acts as an effective metric.
📅13:0013:25, A102
👤︎ João Rosa (University of Tartu, Tartu, Estonia):
Junction conditions in Palatini f(R,T) gravity
We work out the junction conditions for the Palatini \(f(\mathcal{R},T)\) extension of General Relativity, where \(f\) is an arbitrary function of the curvature scalar \(\mathcal{R}\) of an independent connection, and of the trace \(T\) of the stressenergy tensor of the matter fields. We find such conditions on the allowed discontinuities of several geometrical and matter quantities, some of which depart from their metric counterparts, and in turn extend their Palatini \(f(\mathcal{R})\) versions via some new \(T\)dependent terms. Moreover, we also identify some ``exceptional cases" of \(f(\mathcal{R},T)\) Lagrangians such that some of these conditions can be discarded, thus allowing for further discontinuities in \(\mathcal{R}\) and \(T\) and, in contrast with other theories of gravity, they are shown to not give rise to extra components in the matter sector e.g. momentum fluxes and double gravitational layers. We discuss how these junction conditions, together with the nonconservation of the stressenergy tensor ascribed to these theories, may induce nontrivial changes in the shape of specific applications such as traversable thinshell wormholes.
📅13:2513:50, A101
👤︎ Alejandro Jimenez Cano (Institute of Physics, University of Tartu, Tartu, Estonia):
Restrictions in quadratic metricaffine gravity from the stability of the vector sector
In this talk we will revise the stability of the four vector irreducible pieces of the torsion and the nonmetricity tensors in the general quadratic metricaffine Lagrangian in 4 dimensions. This analysis highly constrains the theory and reduces the parameter space of the quadratic curvature part from 16 to 5 parameters. We will also mention the case of WeylCartan gravity, proving that the stability of the vector sector completely fixes the dynamics of the full Lagrangian to just an EinsteinProca theory or pure General Relativity.
📅13:2513:50, A102
👤︎ Aneta Wojnar (Laboratory of Theoretical Physics, Tartu, Estonia):
Matter properties vs gravity
I will review a few last findings related to properties of matter in stellar objects in metricaffine theories of gravity.
📅13:5014:15, A101
💻︎ Damianos Iosifidis (Aristotle University of Thessaloniki, Thessaloniki, Greece):
The Full Quadratic MetricAffine Gravity: Solving for the Affine Connection
We consider the most general Quadratic MetricAffine Gravity setup in the presence of generic matter sources with nonvanishing hypermomentum. The gravitational action consists of all 17 quadratic invariants (both parity even and odd) in torsion and nonmetricity as well as their mixings, along with the terms that are linear in the curvature namely the Ricci scalar and the totally antisymmetric Riemann piece. Adding also a matter sector to the latter we first obtain the field equations for the generalized quadratic Theory. Then, using a recent Theorem, we successfully find the exact form of the affine connection under some quite general nondegeneracy conditions. Finally we shall discuss the consequences and also applications of our result.
📅13:5014:15, A102
💻︎ Adrián CasadoTurrión (Universidad Complutense de Madrid, Madrid, Spain):
Collapsing stars in \(f(R)\) gravity
Gravitational collapse is still poorly understood in the context of \(f(R)\) theories of gravity. The archetypal OppenheimerSnyder model (which is an exact solution of General Relativity) is known to be incompatible with the junction conditions of \(f(R)\) gravity, both in the metric and Palatini formalisms. In this talk, we shall explain how the OppenheimerSnyder construction must be generalised so as to fit within \(f(R)\) models of gravity. By means of a systematic analysis of the relevant junction conditions, we will show that some paradigmatic vacuum metrics cannot represent spacetime outside collapsing stars in \(f(R)\) gravity.
📅14:1514:40, A101
👤︎ Francisco José Maldonado Torralba (University of Tartu, Tartu, Estonia):
ALP dark matter from torsion
In this talk I will explain how the pseudoscalar degree of freedom of the quadratic Poincaré Gauge theory of gravity can act as a dark matter candidate. I will give the parameter space of the theory for which such dark matter candidate can account for all predicted cold dark matter, and constrain such parameters based on current astrophysical observations.
📅14:1514:40, A102
💻︎ Shaswata Chowdhury (Indian Institute of Technology Kanpur, Kanpur, India):
Stable Hydrogenburning Limits in Rapidly Rotating Very Low Mass Objects
We present novel effects of uniform rapid stellar rotation on the minimum mass of stable hydrogen burning in very low mass stars, using an analytic model and relaxing the assumption of spherical symmetry. We obtain an analytic formula for the minimum mass of hydrogen burning as a function of the angular speed of stellar rotation. Further, we show the existence of a maximum mass of stable hydrogen burning in such stars, which is purely an artifact of rapid rotation. The existence of this extremum in mass results in a minimum admissible value of the stellar rotation period of ∼22 minutes, below which a very low mass object does not reach the main sequence, within the ambit of our model. For a given angular speed, we predict a mass range beyond which such an object will not evolve into a mainsequence star.
📅15:0015:25, A101
👤︎ Jorge G. Valcarcel (University of Tartu, Tartu, Estonia):
New black hole solutions with a dynamical traceless nonmetricity tensor in MetricAffine Gravity
In the framework of MetricAffine Gravity, we focus on the dynamical role of the traceless parts of the nonmetricity tensor and construct new static and spherically symmetric black hole solutions with independent shear charges.
📅15:0015:25, A102
💻︎ Surajit Kalita (University of Cape Town, Cape Town, South Africa):
Gravitational wave observation as a tool for validating modified gravity in white dwarfs
After predicting many sub and superChandrasekhar limiting mass white dwarfs from the observations of peculiar type Ia supernovae, researchers proposed various models which can separately explain these two classes of white dwarfs. We have shown that these two peculiar classes of white dwarfs, along with the regular Chandrasekhar white dwarfs, can be explained by a single form of modified gravity, whose effect is significant only in the highdensity regime, and it almost vanishes in the lowdensity regime. Thereby it can explain the violation of the Chandrasekhar masslimit of \(1.4 M_\odot\). However, so far, there is no direct detection of such white dwarfs, and hence it is difficult to single out one specific theory of gravity. In my talk, I’ll show that gravitational wave observation is one of the prominent ways to single out the exact theory of gravity. We estimate the amplitudes of all the relevant polarization modes of gravitational waves for the peculiar and regular white dwarfs and thereby discuss their possible detections in the future through some of the proposed gravitational wave detectors, such as LISA, ALIA, DECIGO, BBO, or Einstein Telescope. This exploration links the theory with possible observations through the gravitational waves in modified gravity.
📅15:2515:50, A101
👤︎ Flavio Bombacigno (Universitat de València, Valencia, Spain):
Spherically symmetric spacetimes in metricaffine ChernSimons gravity
We discuss some recent developments for the metricaffine formulation of ChernSimons gravity, where projective invariance is recovered by enlarging the Pontryagin density definition with nonmetricity depending terms. In particular, we show how analytical solutions for the metricaffine structure can be obtained in spherically symmetric spacetimes, by requiring the absence of dynamical instabilities which we demonstrate to be generated by peculiar components of the affine connection. Finally, we present some exact solutions for the homogeneous and isotropic cosmological background and we discuss in details how the propagation of gravitational waves is affected with respect to the metric formulation.
📅15:2515:50, A102
👤︎ Fernando Izaurieta (University of Concepcion, Concepcion, Chile):
Gravitational Waves in ECSK theory: Robustness of mergers as standard sirens and nonvanishing torsion
The amplitude propagation of gravitational waves in an EinsteinCartanSciammaKibble (ECSK) theory is studied by assuming a dark matter spin tensor sourcing for spacetime torsion at cosmological scales. The analysis focuses on a weaktorsion regime, such that gravitational wave emission, at leading and subleading orders, does not deviate from standard General Relativity. We show that, in principle, the background torsion induced by an eventual dark matter spin component could lead to an anomalous dampening or amplification of the gravitational wave amplitude, after going across a long cosmological distance. The importance of this torsioninduced anomalous propagation of amplitude for binary black hole mergers is assessed. For realistic lateuniverse astrophysical scenarios, the effect is tiny and falls below detection thresholds, even for nearfuture interferometers such as LISA. To detect this effect may not be impossible, but it is still beyond our technological capabilities.
📅15:5016:15, A101
👤︎ Simon Boudet (University of Trento, Trento, Italy):
Black hole perturbations in metricaffine ChernSimons modified gravity
The ChernSimons theory of gravity is obtained by adding the Pontryagin density to the EinsteinHilbert action of General Relativity. This additional term is a topological, parity violating term, which arises in different contexts such as quantum field theory, string theory and loop quantum gravity. When the coupling to the ChernSimons term is promoted to a (pseudo)scalar field, the field equations are modified, offering interesting theoretical insights and new phenomenological predictions. In this talk I will consider the metricaffine formulation of ChernSimons gravity, presenting a generalization of the theory in which the symmetry under projective transformations of the affine connection is restored via a modified Pontryagin density, which still retains its topological character. The theory comes in two versions, depending on whether a kinetic term for the scalar field is included in the action or not. However, in both cases, the scalar field has dynamical character, in contrast to the purely metric version of ChernSimons gravity. I will show how the connection field equations can be solved perturbatively for the torsion and nonmetricity tensors, allowing to study the dynamics of the metric and the scalar field perturbations within the resulting effective scalar tensor theory. As a concrete application I will focus on the evolution of tensor and scalar perturbations on a Schwarzschild background. The parity violating character of the Pontryagin density only affects the axial modes of the black hole, whose quasinormal frequencies are modified with respect to General Relativity and the purely metric version of ChernSimons theory. Finally, I will discuss the properties of the late time section of the gravitational signal, showing how a distinctive signature of metricaffine ChernSimons gravity is encoded in the exponents of the power law tails.
📅15:5016:15, A102
👤︎ Sreekanth Harikumar (National Center for Nuclear Research, Warsaw, Poland):
Lensing of gravitational waves in Palatini f(R) gravity
The planned next generation of detectors like Einstein Telescope, Cosmic Explorer and space based detectors like LISA are likely detect gravitational waves signals more frequently than now. With such an increased frequency of detection we expect some of the signals to be gravitationally lensed. This lensing phenomenon showcases some interesting features like diffraction and formation of beat patterns. Another opportunity that lensing opens up is to test different theories of gravity. In this work we study gravitational lensing in the context of Palatini f(R) gravity using WKB approximation in the geometric optics limit and beyond.
📅16:3016:55, A101
💻︎ Alexey Toporensky (Sternberg astronomical institute, Moscow, Russia):
Multidimension cosmology in GaussBonnet gravity
A successful compactification scenario should explain two, in principle, rather different properties of the multidimensional spacetime. First, we need to show why the evolution of three big dimension is different from the evolution of other dimensions. Second, we need to explain why the 3dimension subspace is almost isotropic one. We present a scenario which address both issures. Starting from rather general totally anisotropic initial condition the evolution of a Universe naturally leads to a product of two isotropic subspaces. This presentation is a brief summary of a set of papers made in collaboration with A.Giakomini, S.Pavluchenko and D. Chirkov.
📅16:3016:55, A102
👤︎ Mercè Guerrero Román (Complutense university of Madrid, Madrid, Spain):
Multiring images of regular compact objects
We discuss the importance of multiring images in the optical appearance of spherically symmetric compact objects, when illuminated by an optically and geometrically thin accretion disk. On the one hand, we shall consider some spherically symmetric black hole and wormhole geometries characterized by the presence of a second critical curve, via a uniparametric family of extensions of the Schwarzschild metric. We will show the presence of additional light rings in the intermediate region between the two critical curves. On the other hand, a subcase of an analytically tractable extension of the Kerr solution, with both a critical curve and an infinite potential barrier at the object’s center for null geodesics. Our results point out to the existence of multiring images with a nonnegligible luminosity in shadow observations.
📅16:5517:20, A101
💻︎ Luiz Garcia de Andrade (uerj, Rio, Brasil and Inst. for Cosmology Croatia):
EinsteinCartanMaxwellHolst Gravity and Chiral Magnetic Dynamos
We review the Einstein Cartan Holst gravity status and introduce the Holst current concept as an additional source for cosmological dynamo amplification
📅16:5517:20, A102
👤︎ Omar Valdivia (Arturo Prat University, Iquique, Chile):
Linear and Secondorder Geometry Perturbations on Spacetimes with Torsion
In order to study gravitational waves in any realistic astrophysical scenario, one must consider geometry perturbations up to second order. Here, we present a general technique for studying linear and quadratic perturbations on a spacetime with torsion. Besides the standard metric mode, a “torsionon” perturbation mode appears. This torsional mode will be able to propagate only in a certain kind of theories.
See Social Program
📅09:1510:15, A106
👤︎ Mikhail Shaposhnikov (Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland):
EinsteinCartan gravity: Inflation and Dark Matter
It is wellknown since the works of Utiyama and Kibble that the gravitational force can be obtained by gauging the Lorentz group, which puts gravity on the same footing as the Standard Model fields. The resulting theory  EinsteinCartan gravity  happens to be very interesting. It may incorporate cosmological inflation driven by the Higgs field of the Standard Model of particle physics. In addition, it contains a fourfermion interaction that originates from torsion associated with spin degrees of freedom. This interaction leads to a novel universal mechanism for producing singlet fermions in the Early Universe. These fermions can play the role of dark matter particles.
📅10:4511:45, A106
💻︎ Gonzalo J. Olmo (University of Valencia  CSIC, Valencia, Spain):
Rotating solutions in RicciBased Gravity theories and the EiBI model
Considering the EiBI gravity model, I will summarize how one can construct axisymmetric solutions in RicciBased Gravity theories (RBGs) using an algebraic correspondence between RBGs and General Relativity. If time permits, physical implications for the counterpart of the KerrNewman black hole coupled to Maxwell electrodynamics will be discussed.
📅13:0013:25, A101
👤︎ Carlo Marzo (Kbfi, Tallinn, Estonia):
Radiatively stable unitarity in higherspin models, and applications in metricaffine gravity
The scrutiny of gravitational theories beyond EinsteinHilbert enjoys a different standard than flat models probed at colliderlevel energies. Of the proposed extensions, only a subset is explicitly required to be free of ghosts. Even in such cases, only dipole ghosts are usually targeted, thus still allowing, in general, wrongsign states to propagate. Moreover, even in rare cases where a thorough spectral analysis is performed, the stability of the resulting action under radiative corrections is uncertain. In this talk, I discuss the strong constraining power of requiring, as standard for lowerspin models, a radiatively stable ghost and tachyonfree action for the paradigmatic scenario of metricaffine gravity. I will describe the role of nonaccidental symmetries and their interplay with diffeomorphism invariance. I will also provide, in a more general way, an overview of the computational challenges on the way of the spectrum of higherspin theories.
📅13:0013:12, A102
👤︎ Sebastian Bahamonde (Tokyo Institute of Technology, Tokyo, Japan):
Black holes in torsional teleparallel gravity
The torsional teleparallel gravity is constructed from a manifold with torsion and zero curvature while respecting the metric compatibility condition. In this talk, I will discuss spherical symmetry in this formalism and present new exact black hole solutions for \(f(T,B)\) gravity and also scalarized solutions from scalartorsion theories of gravity.
📅13:1213:25, A102
👤︎ Christian Pfeifer (University of Bremen, Bremen, Germany):
Teleparallel accretion discs and gravitational waves
In this talk I will present recent results on observables in teleparallel gravity:
accretion discs in f(T)gravity, based on a nonperturbative spherically symmetric solution of the theory
gravitational wave birefringence in new general relativity
📅13:2513:50, A101
👤︎ Oleg Melichev (Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy):
MetricAffine Gravity as an Effective Field Theory
We discuss theories of gravity with independent metric (or frame field) and connection, from the point of view of effective field theory. In general, in addition to the metric, gravitational interactions can be carried by torsion field, or nonmetricity, or both. This theory reduces to the General Relativity at low energies in the natural scenario, but enjoys nontrivial dynamics at high energies as long as dimension four operators, such as curvature squared, are considered. We count such operators of even parity and give explicit bases for the independent ones that contribute to the twopoint function. We then give the decomposition of the linearized action on a complete basis of spin projectors and consider various subclasses of MetricAffine Gravity (MAG) theories. We proceed with discussion of ghost and tachyonic instabilities and construct simple MAGs that contain only a massless graviton and a state of spin/parity 2 or 3 and therefore are stable. Finally, we discuss the renormalisation group flow of the theory.
📅13:2513:50, A102
💻︎ Muzaffer Adak (Pamukkale University, Denizli, Turkey):
Weyl covariance, second clock effect and proper time in theories of symmetric teleparallel gravity
We give a new prescription of parallel transport of a vector tangent to a curve which is invariant under both of a local general coordinate and a Weyl transformation. Thus, since the length of tangent vector does not change during parallel transport along a closed curve in spacetimes with nonmetricity, a second clock effect does not appear in general, not only for the inetgrable Weyl spacetime. We have specially motivated the problem from the point of view of symmetric teleparallel (or MinkowskiWeyl) geometry. We also conclude that as long as nature respects Lorentz symmetry and Weyl symmetry, one can only develop alternative gravity models in the symmetric teleparallel spacetime (Q≠0,T=0,R=0) or the most general nonRiemannian spacetime (Q≠0,T≠0,R≠0).
📅13:5014:15, A101
👤︎ Hardi Veermäe (National Institute of Chemical Physics and Biophysics, Tallinn, Estonia):
Preheating in Palatini R^2 gravity
In the Palatini formalism with an R^2 term, inflation potentials will be flattened to form a plateau in the Einstein frame. In such models, the inflaton field can repeatedly return to this plateau after inflation. This results in an active tachyonic instability which effectively fragments the inflaton condensate in less than an efold. We will discuss tachyonic preheating in Palatini R^2 gravity and in the family of plateau models in general.
📅13:5014:15, A102
👤︎ Philip Schwartz (Leibniz University Hannover, Hannover, Germany):
Teleparallel Newton–Cartan gravity
We discuss a teleparallel version of Newton–Cartan gravity. This theory arises as a formal largespeedoflight limit of the teleparallel equivalent of general relativity (TEGR). Thus, it provides a geometric (‘covariant’) formulation of the Newtonian limit of TEGR, analogous to standard Newton–Cartan gravity being the geometric formulation of the Newtonian limit of general relativity. We show how by a certain gaugefixing the standard formulation of Newtonian gravity can be recovered.
📅14:1514:40, A101
👤︎ Alexandros Karam (National Institute of Chemical Physics and Biophysics, Tallinn, Estonia):
Palatini Inflation
We present various aspects of modified gravity inflationary scenarios when studied in the Palatini formalism.
📅14:1514:40, A102
👤︎ Fidel Fernández Villaseñor (University of Granada, Granada, Spain):
Metricaffine Finslerian gravity
Over the last years, there has been an increasing interest and amount of results in alternative theories of gravitation based on (Lorentz)Finsler geometry. An important achievement has been an equation obtainable by applying the metric variation to a geometric functional [1,2]. In this presentation, based upon [3], we apply the Palatini formalism to the same Finslerian action. We also clarify the structure of the solutions with torsion, extending the classical case [4]. Then, assuming certain regularity at the lightlike directions, we obtain results which provide: A) The uniqueness of the torsionfree (nonlinear) connection, and B) The equivalence of the vacuum equation with the vanishing of the Finslerian Ricci scalar of such connection.
References:
[1] C. Pfeifer and M. R. Wohlfart: Finsler geometric extension of Einstein gravity. Phys. Rev. D (Vol.85, No.6), 2012.
[2] M. Hohmann, C. Pfeifer and N. Voicu: Finsler gravity action from variational completion. Phys. Rev. D 100, 064035 (2019).
[3] M. Á. Javaloyes, M. Sánchez and F. F. Villaseñor: The EinsteinHilbertPalatini formalism in pseudoFinsler geometry. ArXiv eprints, arXiv:2108.03197v2 [math.DG] (2021).
[4] A. N. Bernal et al.: On the (non)uniqueness of the LeviCivita solution in the EinsteinHilbertPalatini formalism. Phys.Lett. B768 (2017) 280287.
📅15:0015:25, A101
👤︎ Margus Saal (University of Tartu, Tartu, Estonia):
The slowroll approximation: accurate enough to estimate different models of inflation?
The spectral index of scalar perturbation n and the ratio of tensortoscalar perturbation r are often used to estimate the consistency of inflation models with the observed results. Extending the theory of gravity to the scalartensor type theory, we show in the presentation how very different models can give the same values for n and r. This suggests that these quantities may not be sufficient to determine whether or not the model is consistent with the observations. We analyze this problem and offer solutions for what and how the model should be further evaluated.
📅15:0015:25, A102
💻︎ Yakov Itin (Jerusalem College of Technology, Jerusalem, Israel):
Energymomentum tensor: Noether vs Hilbert.
In this paper, the relationship between two basic definitions of the energymomentum tensor in field theory is discussed. Hilbert’s definition is based on the variation derivative of the Lagrangian with respect to the metric tensor. By definition, the resulting tensor is symmetric. The conservation of this tensor, on the other hand, requires the use of field equations. Noether’s definition is based on the symmetry of the Lagrangian with respect to the diffeomorphism invariance. This tensor is not symmetric, but it can be symmetrized with the use of the BelinfanteRosenfeld procedure. The conservation of this tensor is selfevident from its definition. Noether’s tensor vanishes on shell modulo a divergence of an arbitrary superpotential. For most essential applications, such as YangMills models, two tensors become equal despite having extremely different features. Moreover, they provide meaningful (and measurable) conserved quantities. In this study, we show that in some natural field models the tensors are actually equivalent. Our analysis is based on a teleparallel spacetime and differentialform representation. We examine the examples of the free pform gauge field theory, the GR in the coframe representation, and the metricfree electrodynamics.
📅15:2515:50, A101
👤︎ Christian Dioguardi (National Institute of Chemical Physics and Biophysics, Harju maakond, Tallinn, Estonia):
Slowroll inflation in Palatini F(R) gravity
We study single field slowroll inflation in the presence of \(F(R)\) gravity in the Palatini formulation. In contrast to metric \(F(R)\), when rewritten in terms of an auxiliary field and moved to the Einstein frame, Palatini \(F(R)\) does not develop a new dynamical degree of freedom. However, it is not possible to solve analytically the constraint equation of the auxiliary field for a general \(F(R)\). We propose a method that allows us to circumvent this issue and compute the inflationary observables. We apply this method to test scenarios of the form \(F(R)=R+αR^n\) and find that, as in the previously known \(n=2\) case, a large \(α\) suppresses the tensortoscalar ratio \(r\). We also find that models with \(F(R)\) increasing faster than \(R^2\) for large \(R\) suffer from numerous problems, with possible implications on the theoretically allowed UV behaviour of such Palatini models.
📅15:2515:50, A102
💻︎ Elena Emtsova (Lomonosov Moscow State university, Sternberg Astronomical Institute, Moscow, Russia):
On conservation laws in STEGR
We derive conservation laws in STEGR with direct application of Noether’s theorem. This approach allows to construct covariant conserved currents, corresponding superpotentials and invariant charges. By calculating currents, one can obtain local characteristics of gravitational field like energy density. Surface integration of superpotentials gives charges which correspond to global quantities of the system like mass, momentum, etc. To test our results for the obtained currents and superpotentials, we calculate the energy density measured by freely falling observer in the simple solutions (Schwartzchild black hole, FRLW) and total mass of the Schwartzchild black hole. We find ambiguities in obtaining the connection, which explicitly affect the values of conserved quantities, and discuss a constructive solution to this problem.
📅15:5016:15, A101
💻︎ Haidar Sheikhahmadi (North West University, Mafikeng, South Africa):
Inflation in Hybrid Metric Palatini Gravity
We consider an inflationary scenario in the framework of the Hybrid Metric Palatini Gravity in which a supplementary term, containing a Palatini type correction is added to the standard GR action. This configuration can be reformulated into the equivalent form of a scalartensor theory, in which a low mass scalar field can explain the observed gravitational phenomenology, by generating longrange forces that pass all the local tests without invoking any kind of screening mechanism, chameleon scenario for instance. We look over the possibility that this effective scalar field may generate the matter content of the early Universe.
📅15:5016:15, A102
👤︎ Débora Aguiar Gomes (Federal University of Ceará, Fortaleza, Brazil):
Energy and entropy in the Geometrical Trinity of gravity
All energy is gravitational energy. That is the consequence of the equivalence principle, according to which gravity is the universal interaction. The physical charges of this interaction have remained undisclosed, but the Advent of the Geometrical Trinity opened a new approach to this foundational problem. Here it is shown to provide a backgroundindependent unification of the previous, noncovariant approaches of BergmannThomson, Cooperstock, Einstein, von Freud, LandauLifshitz, Papapetrou and Weinberg. First, the Noether currents are derived for a generic Palatini theory of gravity coupled with generic matter fields, and then the canonical i.e. the unique charges are robustly derived and analysed, particularly in the metric teleparallel and the symmetric teleparallel versions of General Relativity. These results, and their application to black holes and gravitational waves, are new.
Discussion leader: Adrià Delhom I Latorre
Prof. Davi Rodrigues will speak at the historic Tartu Old Observatory on the topic “Why do galaxies rotate?”
📅09:1510:15, A106
👤︎ Branislav Cvetkovic (Institute of physics, University of Belgrade, Belgrade, Serbia):
Hamiltonian approach to entropy in Poincare gauge theory
The canonical generator \(G\) of local symmetries in Poincare gauge theory is constructed as an integral over a spatial section \(\Sigma\) of spacetime. Its regularity (differentiability) on the phase space is ensured by adding a suitable surface term, an integral over the boundary of at infinity, which represents the asymptotic canonical charge. For black hole solutions, \(\Sigma\) has two boundaries, one at infinity and the other at horizon. It is shown that the canonical charge at horizon defines entropy, whereas the regularity of G implies the first law of black hole thermodynamics. The approach is tested for several black hole types.
📅10:3011:00, A106
👤︎ Tomi Koivisto (University of Tartu, Tallinn, Estland):
ΛCDM theory of cosmology
The constants Λ and the CDM in the standard model of cosmology arise as integration constants in the derivation of Einstein’s equations from the gauge theory of the Lorentz group.
📅11:0011:25, A106
💻︎ Emanuele Orazi (Federal University of Rio Grande do Norte, Natal, Brasil):
Conformal Invariant MetricAffine Gravity Theories
A recent revival of the link between conformal symmetry and projective invariance in the framework of metricaffine gravity theories motivated a systematic study of a general strategy to build a conformal version of any modified gravity. In this oral presentation will be clarified the underlying gauge symmetry associated to conformal invariance and its theoretical and phenomenological implications deriving from the explicit solutions of field equations in the metric affine formalism.
📅11:2511:50, A106
👤︎ Yuri Bonder (Universidad Nacional Autonoma de Mexico, Mexico City, Mexico):
Symmetries in gauge theories of gravity with and without nondynamical fields
I will present a transparent and concise method to write generic gauge theory, including gravity gauge theories, and extract the corresponding symmetries from the Lagrangian equations of motion. This method can be applied to theories where the symmetries are broken by the presence of nondynamical fields. As an example, I will discuss unimodular gravity in the first order formalism, where invariance under diffeomorphisms is partially broken. Still, the method can be used to read off the remaining symmetries. Remarkably, the symmetry algebra was calculated and it is possible to verify that it is has the expected properties.
📅11:5012:15, A106
👤︎ Gerardo GarcíaMoreno (Instituto de Astrofísica de Andalucía, Granada, Spain):
On the differences between General Relativity and Unimodular Gravity
Weyl TransverseDiffeomorphisms (WTDiff) gravity is a theory so closely related to General Relativity (GR) that one can wonder to what extent they are really different. Unimodular gravity can be thought as a simple gauge fixing of WTDiff and hence completely equivalent to it. WTDiff and GR are based on two different gauge symmetries: WTDiff is based on Transverse Diffeomorphisms and Weylrescalings of an auxiliary metric, whereas GR is based on the full group of diffeomorphisms. The formal difference appears due to the existence of a fiduciary background structure, a fixed volume form, in WTDiff theories.
In this talk I will present an overview as complete as possible of all the situations and regimes in which one might suspect that some differences between these two theories might arise. This overview contains analysis in the classical, semiclassical and quantum regimes.
See Social Program
📅09:1510:15, A106
👤︎ Jose Beltran Jimenez (Universidad de Salamanca, Salamanca, Spain):
The harzards in Affinesia: Quicksands and sweet spots
The equivalence principle naturally provides gravity with a geometrical character, thus making the metricaffine framework be a natural land for gravity theories. However, the precise geometry we employ admits a certain flexibility and, in particular, Einstein’s gravity can be equivalently ascribed to the three independent objects that characterise a connection, i.e., curvature, torsion and nonmetricity. After reviewing these three alternative descriptions of gravity, I will uncover how pathologies generally arise beyond these GR equivalents and illustrate with some examples how to get around them.
📅10:4511:10, A106
👤︎ Manuel Hohmann (University of Tartu, Tartu, Estonia):
General cosmologies and their perturbations in teleparallel gravity
Within the framework of teleparallel gravity, a flat affine connection is used as a dynamical field in addition to the metric tensor. Depending on the class of theories, this connection may further be restricted by imposing either vanishing torsion or vanishing nonmetricity. In the field of cosmology, most commonly a particular, simple, homogeneous and isotropic connection has been chosen, and its background dynamics and perturbations have been studied for different theories. While this does lead to a set of cosmological dynamical equations, it is far from being the most general cosmological dynamics in teleparallel gravity. This presentation gives a complete classification of all homogeneous and isotropic teleparallel geometries (general, metric and symmetric), as well as their perturbations. For the latter, gauge transformations and gauge invariant quantities are presented. It is shown that:
 general teleparallel gravity admits two spatially curved branches with three spatially flat limits,
 symmetric teleparallel gravity admits one spatially curved branch with three spatially flat limits,
 metric teleparallel gravity admits two spatially curved branches with one spatially flat limit,
and that the two latter cases arise as limits of the first.
📅11:1011:35, A106
👤︎ Jackson Said (Institute of Space Sciences and Astronomy, Msida, Malta):
Traditional and Novel approaches to model selection in f(T) gravity using recent observational cosmology
Teleparallel gravity offers numerous possible classes of theories and arbitrary models in each class. One such example is f(T) gravity where any functional form of the torsion scalar is included. The problem of reducing the space of viable functions has led to several recent interesting avenues of research. Traditionally, models in theories like f(T) gravity would be chosen to meet specific observational or theoretical conditions, which would then be constrained against various observations using Bayesian methods. Recent works in the literature have proposed the use of machine learning techniques to reverse the way models are selected in theories like f(T) gravity so that observational data can be used to define the functional form of the model. In this talk, I will cover some of these new approaches and discuss how they compare with previous methods.
📅11:3512:00, A106
👤︎ Alexey Golovnev (British University in Egypt, El Sherouk, Cairo, Egypt):
Transferring the troubles from torsion to nonmetricity
It is a very interesting field of modified gravity research now, constructing modifications starting from alternative geometrical foundations. It gives very exciting new angles to look at general relativity, in particular because no simple modifications of this sort appear to be healthy. I will briefly review the foundational issues of modified teleparallel gravity, then discuss modified symmetric teleparallel models, and compare the two approaches.
📅13:0013:25, A101
👤︎ Daniel Blixt (Scuola Superiore Merdionale, Naples, Italy):
Lorentz symmetries in teleparallel theories of gravity
Teleparallel gravity is a peculiar limit in the metric affine frameworks of gravity where curvature is taken to zero and still a classically equivalent to general relativity can be found. In its original formulation teleparallel gravity breaks Lorentz invariance at minimum at the boundary and in its most generic case fully. Later there was a realization that a spin connection can be introduced for which Lorentz transformations of the couple tetrad and spin connection leaves the action invariant. This is referred to as the covariant formulation of teleparallel gravity. In this talk I will give deeper insights of Lorentz symmetries in teleparallel theories of gravity referring to both a simple observation as well as to the Hamiltonian analysis and highlight the relation to physical degrees of freedom.
📅13:0013:25, A102
💻︎ Bivudutta Mishra (BITSPilani, Hyderabad Campus, Hyderabad, India):
Reconstruction of Matter Bounce Cosmology in symmetric teleparallel gravity
In this paper, we have constructed the cosmological model of the universe that shows the bouncing scenario. We have obtained specific form of the function f(Q) that shows the bouncing behavior at the backdrop of homogeneous and isotropic spacetime, Q being the nonmetricity. The dynamics of the model has been studied with the help of critical points and the stability behavior has been discussed.
📅13:2513:50, A101
👤︎ MariaJose Guzman (University of Tartu, Tartu, Estonia):
Canonical structure of symmetric teleparallel and f(Q) gravity
Modified gravities based on nonmetricity of spacetime have gained an increased attention in recent years. In particular, f(Q) gravity models come as the simplest generalization of the symmetric teleparallel equivalent of general relativity, and are intensively used in cosmological applications. However, the question of the number of physical degrees of freedom and their behavior is not clear. In this talk we will review the literature and recent progress on the Hamiltonian formalism for symmetric teleparallel and f(Q) gravity, compare to the controversial case of f(T) gravity, and derive conclusions that might be of help for future research.
📅13:2513:50, A102
👤︎ Laxmipriya Pati (BITS Pilani, Hyderabad, India):
Rip cosmological models in extended symmetric teleparallel gravity
In this work, we have investigated some rip cosmological models in an extended symmetric teleparallel gravity theory. We consider the form f(Q, T) = aQ^m+bT in the Einstein–Hilbert action and expressed the field equations and the dynamical parameters in terms of the nonmetricity ‘Q’. Three rip models such as Little Rip, Big Rip and Pseudo Rip are presented. The energy conditions and the cosmographic parameters are derived and analysed for all these models.
📅13:5014:15, A101
💻︎ Franco Fiorini (Insituto Balseiro & Conicet, S. C. de Bariloche, Argentina):
Remnant symmetries in f(T)like models: lessons from 2D
By constructing twodimensional, nonlocal Lorentz invariant gravitational actions based on the torsion tensor, we discuss the physical meaning of the remnant symmetries associated with the nearhorizon geometry experienced by a radial observer in Schwarzschild spacetime. These symmetries, which represent special or privileged diads, acquire the form of uniformly accelerated (Rindler) observers whose constant acceleration is proportional to the black hole mass M.
📅13:5014:15, A102
💻︎ Simran Arora (Birla Institute of Technology and SciencePilani, Hyderabad Campus, Hyderabad, India):
Constraining effective equation of state in f (Q, T) gravity
New highprecision observations are now possible to constrain different gravity theories. To examine the accelerated expansion of the Universe, we used the newly proposed f(Q,T) gravity, where Q is the nonmetricity, and T is the trace of the energymomentum tensor. The investigation is carried out using a parameterized effective equation of state with two parameters, m and n. We have also considered the linear form of f(Q,T) = Q + b T, where b is constant. By constraining the model with the recently published 1048 Pantheon sample, we were able to find the best fitting values for the parameters b, m, and n. The model appears to be in good agreement with the observations. Finally, we analyzed the behavior of the deceleration parameter and equation of state parameter. The results support the feasibility of f(Q,T) as a promising theory of gravity, illuminating a new direction towards explaining the Universe’s dark sector.
📅14:1514:40, A101
💻︎ Morgan Le Delliou (Lanzhou University, Lanzhou, China):
Teleparallel Gravities as a gauge theories: TEGR and STGR, a work in progress
Initiated with a question on the mathematical nature of the connection in the socalled “translations gauge theory” formulation of Teleparallel Equivalent to General Relativity (TEGR) Theory, our explorations led us to consider a novel approach using a Cartan connection. The mathematically admitted underlying structure of a gauge theory for a symmetry group \(G\) relies on a principal \(G\)bundle on which is chosen a connection (the gauge field). The bundle formalism with connection allows to distinguish in the structure of TEGR as “translations gauge theory” that the algebra of translations is indeed necessary to build the torsion, which could resemble the field strength of that gravity. However, the corresponding field clearly does not present the structure of a connection. Nevertheless, the translation field can be integrated in a Cartan connection, as shown in our approach, which allows to keep the interpretation of the translation field as related to a connection. The coupling to matter can be performed thanks to a Cartan connection and a theorem by Sharpe to obtain a consistent and complete description of TEGR that confirms its difference with the usual structures of gauge theories. The approach to STGR involves a closer examination of bundle reduction and soldering form that appear to mark the specificity of gravity. Although the frame field remains the best candidate for what could be recognised as a gauge field, the introduction of a distinct soldering form through a bundle reduction giving birth to the metric on the base leads to a specific structure. To bring such a framework closer to a theory with a connection will require more investigations.
📅14:1514:40, A102
💻︎ Siddheshwar Kadam (BITSPilani, Hyderabad, India):
Dynamical features of \(f(T,B)\) cosmology
In this paper, we have explored the field equations of \(f(T, B)\) gravity and determined the dynamical parameters with the hyperbolic function of the Hubble parameter. The accelerating behavior has been observed and the behavior of the equation of state parameter indicates the \(\Lambda CDM\) model at a late time. The role of model parameters in assessing accelerating behavior has been emphasized. The stability of the model is analyzed by using scalar perturbation.
📅15:0015:25, A101
👤︎ Ludovic Ducobu (University of Mons, Mons, Belgium):
Scalarized Black Holes in Teleparallel Gravity
If General Relativity [GR] offers an extremely successful framework to describe the gravitational interaction, whose achievements range from the solar system to the cosmological scale, the necessity to question the framework of GR is clear at both the experimental and theoretical levels. Since not all of the current puzzles can be purely reduced to quantum correction problems, this motivates the study of alternative theories of gravitation already at the classical level.
Among the many possible directions one can follow, an interesting one consists in the addition of new degrees of freedom in the theory (in addition to the spacetime metric). In this respect, the simplest candidate is a scalar field. Alternative theories of gravity including a scalar field have attracted a lot of attention in the past decade. This is especially true for Horndeski gravity; the most general scalartensor theory of gravity in 4D, based on the same geometrical framework as GR, including a real scalar field and presenting second order field equations.
The aim of this talk will be to introduce recent results of our research in the context of teleparallel theories of gravity extended by scalar fields. I will start by a short synopsis of the main features of teleparallel theories of gravity compared to metric based theories (especially GR). I will then discuss recent results regarding hairy black holes for some teleparallel theories of gravity endowed with a nonminimally coupled real scalar field.
If time permits, I will comment on how one could possibly extend results obtained for metric based scalartensor theories of gravity using the framework of teleparallel gravity.
📅15:0015:25, A102
💻︎ Armando Aram Reyes Aguilar (Nuclear Sciences Institute, Mexico city, Mexico):
Inhomogeneous solutions in \(f(T,B)\) gravity
In this paper, we explore the possibility to find exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric LemaîtreTolmanBondi (LTB) dust models. We apply to the LTB metric the formalism of TG in its extension to \(f(T,B)\) models, which can be seen as the analogous from the Schwarzschild solution in General Relativity. An exact LTB solution is obtained which is compatible with a specific \(f(T,B)\) model whose observational constraints are cosmologically viable in a standard spatially flat RobertsonWalker geometry.
📅15:2515:45, A101
👤︎ Joosep Lember (University of Tartu, Tartu, Estonia):
Black hole solutions in scalartensor symmetric teleparallel gravity
Symmetric teleparallel gravity is constructed with a nonzero nonmetricity tensor while both torsion and curvature are vanishing. In this framework, we find exact scalarised spherically symmetric static solutions in scalartensor theories built with a nonminimal coupling between the nonmetricity scalar and a scalar field. It turns out that the BocharovaBronnikovMelnikovBekenstein solution has a symmetric teleparallel analogue (in addition to the recently found metric teleparallel analogue), while some other of these solutions describe scalarised black hole configurations that are not known in the Riemannian or metric teleparallel scalartensor case. To aid the analysis we also derive nohair theorems for the theory. Since the symmetric teleparallel scalartensor models also include \(f(Q)\) gravity, we shortly discuss this case and further prove a theorem which says that by imposing that the metric functions are the reciprocal of each other (\(g_{rr}=1/g_{tt}\)), the \(f(Q)\) gravity theory reduces to the symmetric teleparallel equivalent of general relativity (plus a cosmological constant), and the metric takes the (Anti)deSitterSchwarzschild form.
📅15:2515:45, A102
👤︎ Paul Martin Kull (University of Tartu, Tartu, Estonia):
Nonexotic wormholes in \(f(R,T)\) gravity
In this work, stable traversable wormhole models that satisfy at least the null energy condition (NEC) everywhere are developed in the geometric representation of \(f(R,T)\) gravity. The NEC is satisfied both everywhere in the wormhole spacetime and by using the thinshell formalism to match the wormhole spacetime with an exterior vacuum spacetime. In the first case, conditions are determined for the particular forms of the shape and redshift functions \(b(r)\) and \(\zeta(r)\) considered that guarantee that the resulting spacetime satisfies at least the NEC everywhere. In the second case, after deriving the junction conditions for the particular form of the theory used, one finds that the radius \(r_\Sigma\) of the thinshell is not restricted to single values for some values of the throat radius \(r_0\). This allows one to choose \(r_\Sigma\) and \(r_0\) such that the weak energy condition can also be satisfied everywhere.
📅15:4516:10, A101
👤︎ Laur Järv (University of Tartu, Tartu, Estonia):
Spherically symmetric static spacetime in the coincident gauge of symmetric teleparallel gravity
In the context of symmetric teleparallel gravity the coincident gauge denotes a coordinate system where the affine connection vanishes globally and the covariant derivatives reduce to partial derivatives. Despite the allure for computational ease, explicit examples of this are hard to come by. In the talk we consider general metric and affine connection which both are spherically symmetric and static, and transform this configuration into the coincident gauge. We conclude with a comparison to the Weitzenböck gauge in metric teleparallelism, and remarks about the notion of ‘purely inertial connection’.
📅15:4516:10, A102
💻︎ Vesselin Gueorguiev (Institute for Advanced Physical Studies, Sofia, Bulgaria):
Main Results and Current Progress within the Scale Invariant Vacuum Paradigm
A review of the Scale Invariant Vacuum (SIV) idea will be presented as related to Weyl Integrable Geometry [1]. The main results related to SIV and inflation [2], the growth of the density fluctuations [3], and the application of the SIV to scaleinvariant dynamics of Galaxies, MOND, Dark Matter, and the Dwarf Spheroidals [4] will be highlighted.
[1] Gueorguiev, V. G., Maeder, A., The Scale Invariant Vacuum Paradigm: Main Results and Current Progress. Universe 2022, 8 (4) 213; DOI:10.3390/universe8040213 [grqc/2202.08412].
[2] Maeder, A., Gueorguiev, V. G., Scale invariance, horizons, and inflation. MNRAS 504, 4005 (2021) [grqc/2104.09314].
[3] Maeder, A., Gueorguiev, V., G., The growth of the density fluctuations in the scaleinvariant vacuum theory. Phys. Dark Univ. 25, 100315 (2019) [astroph.CO/1811.03495]
[4] Maeder, A.; Gueorguiev, V.G. Scaleinvariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals. MNRAS 492, 2698 (2019) [grqc/2001.04978]
Discussion leader: Christian Pfeifer
See Social Program
📅09:1509:45, A106
👤︎ Davi Rodrigues (Federal University of Espirito Santo (UFES), Vitória, Brazil):
Testing modified gravity rotation curves with the Normalized Additional Velocity method
I will introduce the Normalized Additional Velocity (NAV) method and show how to apply it, with focus on modified gravity (although it can also be useful for dark matter profiles). The method will be illustrated with several models, including \(f(R)\) Palatini, EddingtoninspiredBornInfeld (EiBI), MOND and others. It is a complementary and fast approach to study galaxy rotation curves (RCs) directly from the sample distribution, instead of first performing several individual RC fits. It does not cover all the RC properties, but it focuses on the shape of the nonNewtonian contribution for a given sample (we use 122 SPARC galaxies). A relevant advantage, when applying the method to modified gravity models, is that for several models it is possible to use approximations that circumvent the need for solving modified Poisson equations for each one of the galaxies. Among other results, we show that \(f(R)\) Palatini and EiBI gravities cannot be used to replace dark matter in galaxies, while MOND has reasonable results, although with an issue.
Based on https://arxiv.org/abs/2204.03762 and more recent developments.
📅09:4510:15, A106
💻︎ Emmanuel Saridakis (National Observatory of Athens, Athens, Greece):
Tracing torsional gravity in the early universe: primordial black holes and gravitational waves
There is a huge variety of gravitational modifications constructed for theoretical reasons, namely to alleviate the renormalizability issues of General Relativity, as well as for cosmological reasons, namely to successfully describe the Universe evolution and alleviate possible observational tensions. It is time to start using the rich observational datasets of increasing accuracy in order to distinguish between them. We search for signatures and smoking guns of torsional modified gravity in late and earlytime cosmological observations, focusing on gravitational waves and primordial black holes.
We end the last parallel session with a few comments on previous and possible future meetings.
📅10:4511:10, A101
👤︎ Orest Hrycyna (National Centre for Nuclear Research, Warszawa, Poland):
A new generic and structurally stable cosmological model without singularity
Dynamical systems methods are used to investigate a cosmological model with nonminimally coupled scalar field and asymptotically quadratic potential function. We found that for values of the nonminimal coupling constant parameter \(\frac{3}{16}\lt\xi\lt\frac{1}{4}\) there exists an unstable asymptotic de Sitter state giving rise to nonsingular beginning of universe. The energy density associated with this state depends on value of the nonminimal coupling constant and can be much smaller than the Planck energy density. For \(\xi=\frac{1}{4}\) we found that the initial state is in form of the static Einstein universe. Proposed evolutional model, contrary to the seminal Starobinsky’s model, do not depend on the specific choice of initial conditions in phase space, moreover, a small change in the model parameters do not change the evolution thus the model is generic and structurally stable. The values of the nonminimal coupling constant can indicate for a new fundamental symmetry in the gravitational theory. We show that Jordan frame and Einstein frame formulation of the theory are physically nonequivalent.
📅10:4511:10, A102
💻︎ Monika E. Pietrzyk (University of Exeter, Exeter, United Kingdom):
Covariant HamiltonJacobi Equation for the Teleparallel Equivalent of General Relativity
The covariant De DonderWeyl Hamiltonian theory of the Teleparallel Equivalent of General Relativity is formulated using the methods developed by I. Kanatchikov within his approach of precanonical quantization. Based on the results from the geometric HamiltonJacobi theory for variational problems we derive a covariant HamiltonJacobi equation for TEGR which generalizes the covariant HamiltonJacobi equation for General Relativity which was obtained by Th. De Donder (1930) and P. Hoava (1991). I also comment on the problem of the relation between the canonical HJ equations derived from the canonical ADM formalism and the covariant HJ equations derived from the De DonderWeyl Hamiltonian theory. The covariant HJ equation can be used for numerical simulations or as a test of the classical limit of quantum TEGR, its quasiclassical study and Bohmianlike formulation. Based on my joint paper with C. Barbachoux: ePrint: 2201.01295 [grqc].
📅11:1011:35, A101
💻︎ Nurgissa Myrzakulov (LN Gumilyov Eurasian National University, NurSultan, Kazakhstan):
Symmetric teleparallel f(Q) gravity with nonminimally coupled fermion field
In this work, we explore the symmetric teleparallel \(f(Q)\) gravity, which is nonminimally coupled with the fermion field in the FriedmannRobertsonWalker metric. By using the Lagrange multiplier modified Friedmann equations, Dirac equations for the fermion field are obtained. Using the Noether symmetry method, the form of the coupling between gravity and matter, the selfconsistent potential, the symmetry generators, the form of \(f(Q)\) gravity, and the conserved quantity for this model are determined. Cosmological solutions describe the latetime accelerated expansion of the Universe obtained.
📅11:1011:35, A102
💻︎ Igor Kanatchikov (Natl.Quantum Information Center, Sopot, Poland):
Towards quantum geometric trinity of gravity
We plan to present (i) a reformulation of the classical geometric trinity of gravity which allows discussing quantization of equivalent descriptions of general relativity within a unifying framework, (ii) the covariant Hamiltonian formulation of the trinity based on the polysymplectic formalism and the PoissonGerstenhaber brackets of differential forms, and the Diraclike analysis of constraints, (iii) a quantum formulation of the trinity based on the quantization of the analog of Dirac brackets in the above formalism that leads to three different covariant generalizations of the Schroedinger (or WheelerDewitt) equation for quantum gravity. They treat spacetime dimensions on equal footing and describe quantum geometry in terms of Cliffordalgebravalued amplitudes of spinconnection (in GR) or vielbeins (in TEGR), or metric density (in Coincident GR). We briefly discuss a relation to the canonical ADM formulations and the canonical quantization, the emergence of the classical limit, the nonGaussian statistics of quantum gravitational fluctuations in a cosmological context, a naive estimation of the quantum gravity contribution to the cosmological constant, and the scale when quantumgravitational fluctuations “foam” classical spacetime, which turns out to be significantly subPlanckian.
📅11:3512:00, A101
💻︎ Santosh Lohakare (BITS Pilani, Hyderabad, India):
Cosmological model with time varying deceleration parameter in F(R, G) gravity
In this work, we investigate the dynamical behavior of the Universe in the F(R, G) theory of gravity, where R and G indicate the Ricci scalar and GaussBonnet invariant, respectively. The energy conditions, cosmographic parameters, stability, and the possibility of recreating the mentioned model using a scalar field formalism are all part of our comprehensive research. At late times, the model obtained here exhibits quintessencelike behavior.
📅11:3512:00, A102
💻︎ Abdel Nasser Tawfik (Future University in Egypt (FUE), New Cairo, Egypt):
On possible quantization of metric tensor and affine connection
When the minimal length approach emerging from noncommutative Heisenberg algebra, generalized uncertainty principle, and thereby integrating gravitational fields to this fundamental theory of quantum mechanics (QM) is thoughtfully extended to general relativity (GR), the possible quantization of the fundamental tensor is suggested. This is a complementary term reconciling principles of QM and GR and comprising noncommutative algebra together with maximal spacelike fouracceleration. That quantization compiles with GR as curvature in relativistic eightdimensional spacetime tangent bundle, Finsler spacetime, the generalization of the pseudoRiemannian spacetime, is the recipe applied to derive the quantized metric tensor. This dictates how the affine connection on pseudoRiemannian manifold is straightforwardly quantized. We have discussed the symmetric property of quantized metric tensor and affine connection.
📅12:0012:25, A101
💻︎ Amarkumar Agrawal (Birla Institute of Technology and Science, Pilani, Hyderabad Campus, India, Hyderabad, India):
Matter bounce scenario in the functional form of f(R) gravity
We examined bouncing cosmological models in an isotropic and homogeneous spacetime with the f(R) theory of gravity. The bouncing scale factor was used to study two functional forms of f(R). Along with the cosmographic parameters, the dynamical parameters are calculated and analysed. Both the models’ analyses reveal the presence of bounce. In both models, the violation of strong energy conditions is also shown.
📅12:0012:25, A102
💻︎ Sravan Kumar (Tokyo Institute of Technology, Tokyo, Japan):
Probing quantum gravity and nonlocality through R^2like inflation
Cosmic inflation is an important paradigm of the early Universe which is so far developed in two equivalent ways, either by geometrical modification of Einstein’s general relativity (GR) or by introducing new forms of matter beyond the standard model of particle physics. Starobinsky’s R+R^2 inflation based on a geometric modification of GR is one of the most observationally favorable models of cosmic inflation based on a geometric modification of GR. In this talk, I will discuss in detail the fundamental motivations for Starobinsky inflation and present how certain logical steps in the view of its UV completion lead to the emergence of a gravity theory that is nonlocal in nature. Then I will establish how one can perform studies of the early Universe in the context of nonlocal gravity and what are the observational consequences in the scope of future CMB and gravitational waves. I will discuss in detail how nonlocal R^2like inflation can be observationally distinguishable from the local effective field theories of inflation. Finally, I will comment on the prospects of nonlocal gravity as a promising candidate for quantum gravity.
📅12:2512:45, A101
👤︎ Kärt Soieva (University of Tartu, Tartu, Estonia):
The cooling process of brown dwarfs in Horndeski theory of gravity
In the presentation the cooling process of brown dwarf stars in the framework of DHOST theories will be discussed. The analytical model and its numerical solutions are showcased.