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15 pages, 542 KiB

Open AccessArticle

Avoiding Bias in Measurements of Fundamental Constants from High Resolution Quasar Spectra

by John K. Webb, Chung-Chi Lee and Dinko Milaković

Universe 2022, 8(5), 266; https://doi.org/10.3390/universe8050266 - 27 Apr 2022

Cited by 11 | Viewed by 1799

Abstract

Recent advances in spectroscopic instrumentation and calibration methods dramatically improve the quality of quasar spectra. Supercomputer calculations show that, at high spectral resolution, procedures used in some previous analyses of spacetime variations of fundamental constants are likely to generate spurious measurements, biased systematically [...] Read more.

Recent advances in spectroscopic instrumentation and calibration methods dramatically improve the quality of quasar spectra. Supercomputer calculations show that, at high spectral resolution, procedures used in some previous analyses of spacetime variations of fundamental constants are likely to generate spurious measurements, biased systematically towards a null result. Developments in analysis methods are also summarised and a prescription given for the analysis of new and forthcoming data. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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30 pages, 405 KiB

Open AccessArticle

Ultraviolet Finiteness or Asymptotic Safety in Higher Derivative Gravitational Theories

by Lesław Rachwał

Universe 2022, 8(4), 229; https://doi.org/10.3390/universe8040229 - 8 Apr 2022

Cited by 2 | Viewed by 1791

Abstract

We present and discuss well known conditions for ultraviolet finiteness and asymptotic safety. The requirements for complete absence of ultraviolet divergences in quantum field theories and existence of a non-trivial fixed point for renormalization group flow in the ultraviolet regime are compared based [...] Read more.

We present and discuss well known conditions for ultraviolet finiteness and asymptotic safety. The requirements for complete absence of ultraviolet divergences in quantum field theories and existence of a non-trivial fixed point for renormalization group flow in the ultraviolet regime are compared based on the example of a six-derivative quantum gravitational theory in

d = 4

spacetime dimensions. In this model, it is possible for the first time to have fully UV-finite quantum theory without adding matter or special symmetry, but by inclusion of additional terms cubic in curvatures. We comment on similarities and some apparent differences between the two approaches, but we show that they are both compatible to each other. Finally, we motivate the claim that actually asymptotic safety needs UV-finite models for providing explicit form of the ultraviolet limit of Wilsonian effective actions describing special situations at fixed points. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

13 pages, 1018 KiB

Open AccessArticle

Noncommutativity, Sáez–Ballester Theory and Kinetic Inflation

by S. M. M. Rasouli

Universe 2022, 8(3), 165; https://doi.org/10.3390/universe8030165 - 7 Mar 2022

Cited by 9 | Viewed by 1863

Abstract

This paper presents a noncommutative (NC) version of an extended Sáez–Ballester (SB) theory. Concretely, considering the spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) metric, we propose an appropriate dynamical deformation between the conjugate momenta and, applying the Hamiltonian formalism, obtain deformed equations of motion. In our [...] Read more.

This paper presents a noncommutative (NC) version of an extended Sáez–Ballester (SB) theory. Concretely, considering the spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) metric, we propose an appropriate dynamical deformation between the conjugate momenta and, applying the Hamiltonian formalism, obtain deformed equations of motion. In our model, the NC parameter appears linearly in the deformed Poisson bracket and the equations of the NC SB cosmology. When it goes to zero, we get the corresponding commutative counterparts. Even by restricting our attention to a particular case, where there is neither an ordinary matter nor a scalar potential, we show that the effects of the noncommutativity provide interesting results: applying numerical endeavors for very small values of the NC parameter, we show that (i) at the early times of the universe, there is an inflationary phase with a graceful exit, for which the relevant nominal condition is satisfied; (ii) for the late times, there is a zero acceleration epoch. By establishing an appropriate dynamical framework, we show that the results (i) and (ii) can be obtained for many sets of the initial conditions and the parameters of the model. Finally, we indicate that, at the level of the field equations, one may find a close resemblance between our NC model and the Starobinsky inflationary model. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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8 pages, 365 KiB

Open AccessCommunication

Late Time Acceleration of the Universe from Quantum Gravity

by Xiankai Pang

Universe 2022, 8(3), 163; https://doi.org/10.3390/universe8030163 - 5 Mar 2022

Cited by 1 | Viewed by 1796

Abstract

We show that the accelerating expansion phase of the universe can emerge from the group field theory formalism, a candidate theory of quantum gravity. The cosmological evolution can be extracted from condensate states using the mean field approximation, in a form of modified [...] Read more.

We show that the accelerating expansion phase of the universe can emerge from the group field theory formalism, a candidate theory of quantum gravity. The cosmological evolution can be extracted from condensate states using the mean field approximation, in a form of modified FLRW equations. By introducing an effective equation of state w, we can reveal the relevant features of the evolution and show that, with the proper choice of the parameters, w will approach

- 1

, leading to an accelerating phase dominated by the cosmological constant effectively. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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9 pages, 281 KiB

Open AccessArticle

Bouncing Cosmology in Fourth-Order Gravity

by Marcello Miranda, Daniele Vernieri, Salvatore Capozziello and Francisco S. N. Lobo

Universe 2022, 8(3), 161; https://doi.org/10.3390/universe8030161 - 4 Mar 2022

Cited by 4 | Viewed by 1718

Abstract

The Big Bang initial singularity problem can be solved by means of bouncing solutions. In the context of extended theories of gravity, we will look for covariant effective actions whose field equations contain up to fourth-order derivatives of the metric tensor. In finding [...] Read more.

The Big Bang initial singularity problem can be solved by means of bouncing solutions. In the context of extended theories of gravity, we will look for covariant effective actions whose field equations contain up to fourth-order derivatives of the metric tensor. In finding such bouncing solutions, we will make use of an order reduction technique based on a perturbative approach. Reducing the order of the field equations to second-order, we are able to find solutions which are perturbatively close to General Relativity. We will build the covariant effective actions of the resulting order reduced theories. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

11 pages, 471 KiB

Open AccessArticle

Testing Screening Mechanisms with Mass Profiles of Galaxy Clusters

by Lorenzo Pizzuti

Universe 2022, 8(3), 157; https://doi.org/10.3390/universe8030157 - 1 Mar 2022

Cited by 1 | Viewed by 1758

Abstract

We present MG-MAMPOSSt, a license-free code to constrain modified gravity models by reconstructing the mass profile of galaxy clusters with the kinematics of the cluster’s member galaxies. We describe the main features of the code and we show the capability of the [...] Read more.

We present MG-MAMPOSSt, a license-free code to constrain modified gravity models by reconstructing the mass profile of galaxy clusters with the kinematics of the cluster’s member galaxies. We describe the main features of the code and we show the capability of the method when the kinematic information is combined with lensing data. We discuss recent results and forecasts on two classes of models currently implemented in the code, characterized by different screening mechanisms, namely, chameleon and Vainshtein screening. We further explore the impact of possible systematics in view of application to the data from upcoming surveys. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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6 pages, 281 KiB

Open AccessCommunication

Can Dark Energy Emerge from a Varying G and Spacetime Geometry?

by Ekim Taylan Hanımeli, Isaac Tutusaus, Brahim Lamine and Alain Blanchard

Universe 2022, 8(3), 148; https://doi.org/10.3390/universe8030148 - 25 Feb 2022

Cited by 2 | Viewed by 2129

Abstract

The accelerated expansion of the universe implies the existence of an energy contribution known as dark energy. Associated with the cosmological constant in the standard model of cosmology, the nature of this dark energy is still unknown. We will discuss an alternative gravity [...] Read more.

The accelerated expansion of the universe implies the existence of an energy contribution known as dark energy. Associated with the cosmological constant in the standard model of cosmology, the nature of this dark energy is still unknown. We will discuss an alternative gravity model in which this dark energy contribution emerges naturally, as a result of allowing for a time-dependence on the gravitational constant, G, in Einstein’s field equations. With this modification, Bianchi’s identities require an additional tensor field to be introduced so that the usual conservation equation for matter and radiation is satisfied. The equation of state of this tensor field is obtained using additional constraints, coming from the assumption that this tensor field represents the space-time response to the variation of G. We will also present the predictions of this model for the late-universe data, and show that the energy contribution of this new tensor is able to explain the accelerated expansion of the universe without the addition of a cosmological constant. Unlike many other alternative gravities with varying gravitational strength, the predicted G evolution is also consistent with local observations and therefore this model does not require screening. We will finish by discussing possible other implications this approach might have for cosmology and some future prospects. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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12 pages, 391 KiB

Open AccessArticle

Gravastars with Kuchowicz Metric in Energy-Momentum Squared Gravity

by Saba Naz and Muhammad Sharif

Universe 2022, 8(3), 142; https://doi.org/10.3390/universe8030142 - 22 Feb 2022

Cited by 11 | Viewed by 1894

Abstract

This paper investigates the geometry of a gravitational vacuum star (also known as a gravastar) from the perspective of

f (R, T^{2})

gravity. The gravastar can be treated as a black hole substitute with three domains: (i) the inner [...] Read more.

This paper investigates the geometry of a gravitational vacuum star (also known as a gravastar) from the perspective of

f (R, T^{2})

gravity. The gravastar can be treated as a black hole substitute with three domains: (i) the inner domain, (ii) the intrinsic shell, and (iii) the outer domain. We examine these geometries using Kuchowicz ansatz for temporal metric function corresponding to a specific

f (R, T^{2})

model. We compute a nonsingular radial metric potential for both the interior and intermediate domains. The matching of these domains with exterior Schwarzschild vacuum results in boundary conditions that assist in the evaluation of unknown constants. Finally, we examine various attributes of gravastar domains, such as the equation of state parameter, proper length, energy, and surface redshift. We conclude that the gravastar model is a viable alternative to the black hole in the background of this gravity. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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7 pages, 365 KiB

Open AccessCommunication

Constraining MOdified Gravity with the S2 Star

by Riccardo Della Monica, Ivan de Martino and Mariafelicia de Laurentis

Universe 2022, 8(2), 137; https://doi.org/10.3390/universe8020137 - 21 Feb 2022

Cited by 10 | Viewed by 1773

Abstract

We have used publicly available kinematic data for the S2 star to constrain the parameter space of MOdified Gravity. Integrating geodesics and using a Markov Chain Monte Carlo algorithm, we have provided the first constraint on the scales of the Galactic Centre for [...] Read more.

We have used publicly available kinematic data for the S2 star to constrain the parameter space of MOdified Gravity. Integrating geodesics and using a Markov Chain Monte Carlo algorithm, we have provided the first constraint on the scales of the Galactic Centre for the parameter

α

of the theory, which represents the fractional increment of the gravitational constant G with respect to its Newtonian value. Namely,

α ≲ 0.662

at 99.7% confidence level (where

α = 0

reduces the theory to General Relativity). Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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20 pages, 2876 KiB

Open AccessArticle

Study of Decoupled Anisotropic Solutions in f(R, T, R_ρηT^ρη) Theory

by Tayyab Naseer and Muhammad Sharif

Universe 2022, 8(2), 62; https://doi.org/10.3390/universe8020062 - 19 Jan 2022

Cited by 39 | Viewed by 2055

Abstract

In this paper, we consider isotropic solution and extend it to two different exact well-behaved spherical anisotropic solutions through minimal geometric deformation method in

f (R, T, R_{ρ η} T^{ρ η})

gravity. We only deform the radial [...] Read more.

In this paper, we consider isotropic solution and extend it to two different exact well-behaved spherical anisotropic solutions through minimal geometric deformation method in

f (R, T, R_{ρ η} T^{ρ η})

gravity. We only deform the radial metric component that separates the field equations into two sets corresponding to their original sources. The first set corresponds to perfect matter distribution while the other set exhibits the effects of additional source, i.e., anisotropy. The isotropic system is resolved by assuming the metric potentials proposed by Krori-Barua while the second set needs one constraint to be solved. The physical acceptability and consistency of the obtained solutions are analyzed through graphical analysis of effective matter components and energy bounds. We also examine mass, surface redshift and compactness of the resulting solutions. For particular values of the decoupling parameter, our both solutions turn out to be viable and stable. We conclude that this curvature-matter coupling gravity provides more stable solutions corresponding to a self-gravitating geometry. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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16 pages, 800 KiB

Open AccessArticle

Vacuum Energy in Saez-Ballester Theory and Stabilization of Extra Dimensions

by Pheiroijam Suranjoy Singh and Kangujam Priyokumar Singh

Universe 2022, 8(2), 60; https://doi.org/10.3390/universe8020060 - 18 Jan 2022

Cited by 6 | Viewed by 2369

Abstract

In this work, we study a spherically symmetric metric in 5D within the framework of Saez-Ballester Theory, where minimal dark energy-matter interaction occurs. We predict that the expanding isotropic universe will be progressively DE dominated. We estimate few values of the deceleration parameter, [...] Read more.

In this work, we study a spherically symmetric metric in 5D within the framework of Saez-Ballester Theory, where minimal dark energy-matter interaction occurs. We predict that the expanding isotropic universe will be progressively DE dominated. We estimate few values of the deceleration parameter, very close to the recently predicted values. We obtain the value of the DE EoS parameter as

ω = - 1

. Additionally, we measure the value of the overall density parameter as

Ω = 0.97 (\approx

1), in line with the notion of a close to or nearly (not exactly) flat universe. We predict that the model universe starts with the Big-Bang and ends at the Big Freeze singularity. In general, we cannot find conditions for stabilization of extra dimensions in general relativity, and all dimensions want to be dynamical. Here, we present two possible conditions to solve this stabilization problem in general relativity. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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10 pages, 1177 KiB

Open AccessCommunication

One-Point Statistics Matter in Extended Cosmologies

by Alex Gough and Cora Uhlemann

Universe 2022, 8(1), 55; https://doi.org/10.3390/universe8010055 - 17 Jan 2022

Cited by 6 | Viewed by 2318

Abstract

The late universe contains a wealth of information about fundamental physics and gravity, wrapped up in non-Gaussian fields. To make use of as much information as possible, it is necessary to go beyond two-point statistics. Rather than going to higher-order N-point correlation [...] Read more.

The late universe contains a wealth of information about fundamental physics and gravity, wrapped up in non-Gaussian fields. To make use of as much information as possible, it is necessary to go beyond two-point statistics. Rather than going to higher-order N-point correlation functions, we demonstrate that the probability distribution function (PDF) of spheres in the matter field (a one-point function) already contains a significant amount of this non-Gaussian information. The matter PDF dissects different density environments which are lumped together in two-point statistics, making it particularly useful for probing modifications of gravity or expansion history. Our approach in Cataneo et al. 2021 extends the success of Large Deviation Theory for predicting the matter PDF in

Λ

CDM in these “extended” cosmologies. A Fisher forecast demonstrates the information content in the matter PDF via constraints for a Euclid-like survey volume combining the 3D matter PDF with the 3D matter power spectrum. Adding the matter PDF halves the uncertainties on parameters in an evolving dark energy model, relative to the power spectrum alone. Additionally, the matter PDF contains enough non-linear information to substantially increase the detection significance of departures from General Relativity, with improvements up to six times the power spectrum alone. This analysis demonstrates that the matter PDF is a promising non-Gaussian statistic for extracting cosmological information, particularly for beyond

Λ

CDM models. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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17 pages, 2366 KiB

Open AccessArticle

Estimating the Cosmological Constant from Shadows of Kerr–de Sitter Black Holes

by Misba Afrin and Sushant G. Ghosh

Universe 2022, 8(1), 52; https://doi.org/10.3390/universe8010052 - 16 Jan 2022

Cited by 20 | Viewed by 2657

Abstract

The Event Horizon Telescope collaboration has revealed the first direct image of a black hole, as per the shadow of a Kerr black hole of general relativity. However, other Kerr-like rotating black holes of modified gravity theories cannot be ignored, and they are [...] Read more.

The Event Horizon Telescope collaboration has revealed the first direct image of a black hole, as per the shadow of a Kerr black hole of general relativity. However, other Kerr-like rotating black holes of modified gravity theories cannot be ignored, and they are essential as they offer an arena in which these theories can be tested through astrophysical observation. This motivates us to investigate asymptotically de Sitter rotating black holes wherein interpreting the cosmological constant

Λ

as the vacuum energy leads to a deformation in the vicinity of a black hole—new Kerr–de Sitter solution, which has a richer geometric structure than the original one. We derive an analytical formula necessary for the shadow of the new Kerr–de Sitter black holes and then visualize the shadow of black holes for various parameters for an observer at given coordinates

(r_{0}, θ_{0})

in the domain

(r_{0}, r_{c})

and estimate the cosmological constant

Λ

from its shadow observables. The shadow observables of the new Kerr–de Sitter black holes significantly deviate from the corresponding observables of the Kerr–de Sitter black hole over an appreciable range of the parameter space. Interestingly, we find a finite parameter space for (

Λ

, a) where the observables of the two black holes are indistinguishable. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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Review

Jump to: Research

11 pages, 315 KiB

Open AccessReview

Moffat MOdified Gravity (MOG)

by Sreekanth Harikumar

Universe 2022, 8(5), 259; https://doi.org/10.3390/universe8050259 - 24 Apr 2022

Viewed by 2210

Abstract

Scalar Tensor Vector Gravity (STVG) or MOdified Gravity (MOG) is a metric theory of gravity with dynamical scalar fields and a massive vector field introduced in addition to the metric tensor. In the weak field approximation, MOG modifies the Newtonian acceleration with a [...] Read more.

Scalar Tensor Vector Gravity (STVG) or MOdified Gravity (MOG) is a metric theory of gravity with dynamical scalar fields and a massive vector field introduced in addition to the metric tensor. In the weak field approximation, MOG modifies the Newtonian acceleration with a Yukawa-like repulsive term due to a Maxwell–Proca type Lagrangian. This associates matter with a fifth force and a modified equation of motion. MOG has been successful in explaining galaxy rotation curves, cosmological observations and all other solar system observations without the need for dark matter. In this article, we discuss the key concepts of MOG theory. Then, we discuss existing observational bounds on MOG weak field parameters. In particular, we will present our original results obtained from the X-COP sample of galaxy clusters. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

22 pages, 5361 KiB

Open AccessReview

How the Big Bang Ends Up Inside a Black Hole

by Enrique Gaztanaga

Universe 2022, 8(5), 257; https://doi.org/10.3390/universe8050257 - 21 Apr 2022

Cited by 16 | Viewed by 4467

Abstract

The standard model of cosmology assumes that our Universe began 14 Gyrs (billion years) ago from a singular Big Bang creation. This can explain a vast range of different astrophysical data from a handful of free cosmological parameters. However, we have no direct [...] Read more.

The standard model of cosmology assumes that our Universe began 14 Gyrs (billion years) ago from a singular Big Bang creation. This can explain a vast range of different astrophysical data from a handful of free cosmological parameters. However, we have no direct evidence or fundamental understanding of some key assumptions: Inflation, Dark Matter and Dark Energy. Here we review the idea that cosmic expansion originates instead from gravitational collapse and bounce. The collapse generates a Black Hole (BH) of mass

M ≃ 5 \times 10^{22} M_{⊙}

that formed 25 Gyrs ago. As there is no pressure support, the cold collapse can continue inside in free fall until it reaches atomic nuclear saturation (GeV), when is halted by Quantum Mechanics, as two particles cannot occupy the same quantum state. The collapse then bounces like a core-collapse supernovae, producing the Big Bang expansion. Cosmic acceleration results from the BH event horizon. During collapse, perturbations exit the horizon to re-enter during expansion, giving rise to the observed universe without the need for Inflation or Dark Energy. Using Ockham’s razor, this makes the BH Universe (BHU) model more compelling than the standard singular Big Bang creation. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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12 pages, 1079 KiB

Open AccessReview

The Scale Invariant Vacuum Paradigm: Main Results and Current Progress

by Vesselin G. Gueorguiev and Andre Maeder

Universe 2022, 8(4), 213; https://doi.org/10.3390/universe8040213 - 27 Mar 2022

Cited by 4 | Viewed by 1879

Abstract

We present a summary of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to the standard Einstein General Relativity (EGR). After a brief review of the mathematical framework, we will [...] Read more.

We present a summary of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to the standard Einstein General Relativity (EGR). After a brief review of the mathematical framework, we will highlight the main results related to inflation within the SIV, the growth of the density fluctuations, and the application of the SIV to scale-invariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals. The possible connection between the weak-field SIV equations and the notion of un-proper time parametrization within the reparametrization paradigm is also discussed. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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17 pages, 841 KiB

Open AccessReview

Compact Objects in Alternative Gravities

by Jose Luis Blázquez-Salcedo, Burkhard Kleihaus and Jutta Kunz

Universe 2022, 8(3), 153; https://doi.org/10.3390/universe8030153 - 28 Feb 2022

Cited by 7 | Viewed by 2670

Abstract

We address neutron stars and black holes in alternative gravities, after recalling their basic properties in General Relativity. Among the plethora of interesting alternative gravities we here focus on an interesting set of scalar-tensor theories. We discuss the phenomenon of spontaneous scalarization, that [...] Read more.

We address neutron stars and black holes in alternative gravities, after recalling their basic properties in General Relativity. Among the plethora of interesting alternative gravities we here focus on an interesting set of scalar-tensor theories. We discuss the phenomenon of spontaneous scalarization, that is, matter induced for neutron stars and curvature induced for black holes. Along with other relevant physical properties, we address the quasi-normal modes of these compact objects. In particular, we consider universal relations of neutron stars to largely reduce the dependence on the equation of state, and we briefly address the shadow of black holes. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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13 pages, 323 KiB

Open AccessReview

Graviton Mass in the Era of Multi-Messenger Astronomy

by Aleksandra Piórkowska-Kurpas

Universe 2022, 8(2), 83; https://doi.org/10.3390/universe8020083 - 27 Jan 2022

Cited by 4 | Viewed by 2058

Abstract

The idea of massive graviton plays a fundamental role in modern physics as a landmark of most scenarios related to modified gravity theories. Limits on graviton mass can be obtained through different methods, using all the capabilities of multi-messenger astronomy available today. In [...] Read more.

The idea of massive graviton plays a fundamental role in modern physics as a landmark of most scenarios related to modified gravity theories. Limits on graviton mass can be obtained through different methods, using all the capabilities of multi-messenger astronomy available today. In this paper, we consider some emerging opportunities. In particular, modified relativistic dispersion relations of massive gravitons may lead to changes in the travel time of gravitational waves (GWs) emitted from distant astrophysical objects. Strong gravitational lensing of signals from a carefully selected class of extra-galactic sources such as compact object binaries (actually, binary neutron stars) is predicted to play an important role in this context. Comparing time delays between images of the lensed GW signal and its electromagnetic (EM) counterpart may be a new model-independent strategy (proposed by us in X.-L. Fan et al., 2017), which is especially promising in light of the fruitful observing runs of interferometric GW detectors, resulting in numerous GW signals. In addition to this direct, kinematic method, one can use an indirect, static method. In this approach, the non-zero graviton mass would modify estimates of the total cluster mass via a Yukawa term, influencing the Newtonian potential. In A. Piórkowska-Kurpas et al., 2022, using the X-COP galaxy cluster sample, we obtained

m_{g} < (4.99 - 6.79) \times 10^{- 29}

eV (at

95 %

C.L.), which is one of the best available constraints. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

11 pages, 352 KiB

Open AccessReview

Polynomial Affine Model of Gravity in Three-Dimensions

by Oscar Castillo-Felisola, Bastian Grez, Oscar Orellana, Jose Perdiguero, Francisca Ramirez, Aureliano Skirzewski and Alfonso R. Zerwekh

Universe 2022, 8(2), 68; https://doi.org/10.3390/universe8020068 - 23 Jan 2022

Cited by 4 | Viewed by 2259

Abstract

In this work, we explore a three-dimensional formulation of the polynomial affine model of gravity, which is a model that extends general relativity by relaxing the equivalence principle through the exclusion of the metric from the set of fundamental fields. In particular, in [...] Read more.

In this work, we explore a three-dimensional formulation of the polynomial affine model of gravity, which is a model that extends general relativity by relaxing the equivalence principle through the exclusion of the metric from the set of fundamental fields. In particular, in an attempt to gain insight of the role of the torsion and nonmetricity in the gravitational models, we consider homogeneous and isotropic cosmological models, for which their solutions are classified in a decisions tree. We also show a few of these explicit solutions that allow the definition of (alternative/emergent) metrics derived from the connection. Full article

(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)

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