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36 pages, 2722 KB

Open AccessArticle

Gravitational Baryogenesis in Energy-Momentum Squared Gravity

by David S. Pereira, Francisco S. N. Lobo and José Pedro Mimoso

Universe 2026, 12(9), 267; https://doi.org/10.3390/universe12090267 - 1 Sep 2026

Viewed by 204

Abstract

We demonstrate that the matter sector itself can drive baryogenesis in energy-momentum squared gravity,

f (R, T^{2})

with

T^{2} \equiv T_{μ ν} T^{μ ν}

. High-density matter corrections provide new time-dependent sources for the baryon asymmetry [...] Read more.

We demonstrate that the matter sector itself can drive baryogenesis in energy-momentum squared gravity,

f (R, T^{2})

with

T^{2} \equiv T_{μ ν} T^{μ ν}

. High-density matter corrections provide new time-dependent sources for the baryon asymmetry through derivative couplings to

T^{2}

and to the full combination

f (R, T^{2})

. Notably, the decoupling temperature is not treated as a free parameter; instead, it is fixed by the freeze-out of the Weinberg

B - L

-violating operator, directly linking the asymmetry to the light-neutrino mass scale and to the modified expansion history. Analyzing representative powers

n = 1 / 4

,

n = 1 / 2

,

n = 5 / 8

, and

n = 1

, we find that entropy evolution sharply distinguishes the models. The

n = 1 / 4

branch cannot serve as a self-contained radiation-era model, the

n = 1 / 2

branch is entropy-safe but too weak to reproduce the observed asymmetry, and the

n = 1

branch survives only after entropy dilution. Remarkably, the

n = 5 / 8

branch provides the cleanest viable realization, generating the observed baryon-to-entropy ratio with controlled effective-field-theory hierarchies. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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16 pages, 614 KB

Open AccessArticle

Gravitational Lensing by k − n Generalized Black-Bounce Space-Times

by Claudio Furtado, Antonio L. A. Moreira, Jose R. Nascimento, Albert Yu. Petrov and Paulo J. Porfírio

Universe 2026, 12(8), 220; https://doi.org/10.3390/universe12080220 - 25 Jul 2026

Viewed by 992

Abstract

We study gravitational lensing by

k - n

generalized black-bounce space-times both in regimes of weak and strong field approximations. These metrics interpolate between regular black holes and one-way or traversable wormholes. First, we investigate the light-like geodesic trajectories and derive an analytical [...] Read more.

We study gravitational lensing by

k - n

generalized black-bounce space-times both in regimes of weak and strong field approximations. These metrics interpolate between regular black holes and one-way or traversable wormholes. First, we investigate the light-like geodesic trajectories and derive an analytical expression for the deflection angle in terms of the bounce parameter in the weak-field gravitational regime. We then turn to the strong-field gravitational regime and display the behavior of the bending angle as a function of both the impact parameter and the bounce parameter. Next, using the lens equations, we analyze how the observables for Sagittarius A* behave concerning the bounce parameter. We obtain the shadow’s radii for some black-bounce metrics and plot the graph of their sizes, comparing them with the Schwarzschild one. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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14 pages, 1076 KB

Open AccessArticle

Higher-Dimensional Quantum-Corrected Oppenheimer–Snyder Model with a Cosmological Constant

by Shudi Jiang, Jianhui Lin and Xiangdong Zhang

Universe 2026, 12(6), 168; https://doi.org/10.3390/universe12060168 - 9 Jun 2026

Viewed by 457

Abstract

We extended the higher-dimensional quantum Oppenheimer–Snyder model to the case with a cosmological constant. For the AdS case, we discuss its thermodynamic properties in extended phase space formalism and make a comparison with classical black holes. For quantum-corrected small black holes in AdS [...] Read more.

We extended the higher-dimensional quantum Oppenheimer–Snyder model to the case with a cosmological constant. For the AdS case, we discuss its thermodynamic properties in extended phase space formalism and make a comparison with classical black holes. For quantum-corrected small black holes in AdS spacetime, the temperature no longer diverges but tends to zero. Additionally, the heat capacity exhibits characteristic behavior indicative of an extra phase transition induced by quantum corrections, highlighting the profound impact of quantum effects on black hole thermodynamics. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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13 pages, 521 KB

Open AccessArticle

Earthquakes as Probing Tools for Gravity Theories

by Aleksander Kozak and Aneta Wojnar

Universe 2026, 12(6), 155; https://doi.org/10.3390/universe12060155 - 26 May 2026

Viewed by 415

Abstract

We propose a novel method for testing gravity models using seismic waves’ velocities. By imposing observational constraints on Earth’s moment of inertia and mass, we rigorously limit the gravitational models’ parameters within a

2 σ

accuracy. Our method, taking the PREM model as [...] Read more.

We propose a novel method for testing gravity models using seismic waves’ velocities. By imposing observational constraints on Earth’s moment of inertia and mass, we rigorously limit the gravitational models’ parameters within a

2 σ

accuracy. Our method, taking the PREM model as our reference and assuming its viability, constrains the parameters governing additional terms to the General Relativity Lagrangian to the following ranges:

- 2 \times 10^{9} ≲ β ≲ 10^{9} m^{2}

for Palatini

f (R)

gravity,

- 8 \times 10^{9} ≲ ϵ ≲ 4 \times 10^{9} m^{2}

for Eddington-inspired Born–Infeld gravity, and

- 10^{- 3} ≲ Υ ≲ 10^{- 3}

for Degenerate Higher-Order Scalar–Tensor theories. We also discuss potential avenues to enhance the proposed method, aiming to impose even tighter constraints on gravity models. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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20 pages, 2013 KB

Open AccessArticle

Thermodynamic Properties and Shadow of a New, Improved Schwarzschild Black Hole in the Infrared Limit

by Celio Rodrigues Muniz, Jonathan Alves Rebouças, Francisco Bento Lustosa, Francisco Tiago Barboza Sampaio and Leonardo Tavares de Oliveira

Universe 2026, 12(4), 96; https://doi.org/10.3390/universe12040096 - 28 Mar 2026

Viewed by 542

Abstract

In this work, we propose a modified Schwarzschild geometry inspired by the Asymptotic Safety approach to quantum gravity, in which the Newtonian coupling becomes a running quantity depending on the radial coordinate. We employ an infrared cutoff at the proper distance and obtain [...] Read more.

In this work, we propose a modified Schwarzschild geometry inspired by the Asymptotic Safety approach to quantum gravity, in which the Newtonian coupling becomes a running quantity depending on the radial coordinate. We employ an infrared cutoff at the proper distance and obtain a new quantum-corrected black hole metric. We provide a thermodynamical analysis, first using standard methods and then proceeding to a geometrothermodynamical study of the phase space and to a topological analysis of phase transitions. We also calculate the grey-body factors of our solution, providing exact lower bounds in the quantum-corrected transmission coefficients. Finally, we present the shadow size and intensity profile of our solution, showing its consistency with current observational constraints. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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24 pages, 2114 KB

Open AccessEditor’s ChoiceArticle

Modified Teleparallel f(T) Gravity, DESI BAO and the H₀ Tension

by Mariam Bouhmadi-López, Carlos G. Boiza, Maria Petronikolou and Emmanuel N. Saridakis

Universe 2026, 12(3), 81; https://doi.org/10.3390/universe12030081 - 14 Mar 2026

Cited by 8 | Viewed by 633

Abstract

We investigate whether late-time modifications of gravity in the teleparallel framework can impact the current tension in the Hubble constant

H_{0}

, focusing on

f (T)

cosmology as a minimal and well-controlled extension of General Relativity. We consider three representative [...] Read more.

We investigate whether late-time modifications of gravity in the teleparallel framework can impact the current tension in the Hubble constant

H_{0}

, focusing on

f (T)

cosmology as a minimal and well-controlled extension of General Relativity. We consider three representative

f (T)

parametrisations that recover the teleparallel equivalent of General Relativity at early times and deviate from it only in late epochs. The models are confronted with unanchored Pantheon+ Type Ia supernovae, DESI DR2 baryon acoustic oscillations, compressed Planck cosmic microwave background distance priors, and redshift-space distortion data, allowing us to jointly probe the background expansion and the growth of cosmic structures. Two of the three models partially shift the inferred value of

H_{0}

towards local measurements, while the third worsens the discrepancy. This behaviour is directly linked to the effective torsional dynamics, with phantom-like regimes favouring higher

H_{0}

values and quintessence-like regimes producing the opposite effect. A global statistical comparison shows that the minimal

f (T)

extensions considered here are not favoured over ΛCDM by the combined data. Nevertheless, our results demonstrate that late-time torsional modifications can non-trivially redistribute current cosmological tensions among the background and growth sectors. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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18 pages, 784 KB

Open AccessArticle

Newtonian Fractional-Dimension Gravity and the Mass-Dimension Field Equation

by Gabriele U. Varieschi

Universe 2025, 11(12), 388; https://doi.org/10.3390/universe11120388 - 24 Nov 2025

Viewed by 1410

Abstract

We resume our analysis of Newtonian Fractional-Dimension Gravity (NFDG), an alternative gravitational model that does not require the dark matter (DM) paradigm. We add three more galaxies (NGC 6946, NGC 3198, NGC 2841) to the catalog of those studied with NFDG methods. Once [...] Read more.

We resume our analysis of Newtonian Fractional-Dimension Gravity (NFDG), an alternative gravitational model that does not require the dark matter (DM) paradigm. We add three more galaxies (NGC 6946, NGC 3198, NGC 2841) to the catalog of those studied with NFDG methods. Once again, NFDG can successfully reproduce the observed rotation curves by using a variable fractional dimension

D (R)

, as with the nine other galaxies previously studied with these methods. In addition, we introduce a mass-dimension field equation for our model, which is capable of deriving the fractional mass dimension

D_{m} (R)

from a single equation, as opposed to the previous

D (R)

, which was obtained simply by matching the experimental rotational velocity data for each galaxy. While the NFDG predictions computed with this new

D_{m} (R)

dimension are not as accurate as those based on the original

D (R)

, they nevertheless confirm the validity of our fractional-dimension approach. Three previously studied galaxies (NGC 7814, NGC 6503, NGC 3741) were analyzed again with these new methods, and their structure was confirmed to be free from any dark matter components. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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11 pages, 268 KB

Open AccessArticle

Neutron Reflectometry and Short-Range Modifications of Gravity

by Jesriel Matias Rocha and Fábio Dahia

Universe 2025, 11(9), 281; https://doi.org/10.3390/universe11090281 - 22 Aug 2025

Viewed by 1364

Abstract

Using the precise measurements of the scattering length of neutron–matter interaction obtained through the method of neutron reflectometry by gravity, we establish new empirical constraints on deviations from the standard behavior of the gravitational interaction at short distances predicted by large extra-dimensional models. [...] Read more.

Using the precise measurements of the scattering length of neutron–matter interaction obtained through the method of neutron reflectometry by gravity, we establish new empirical constraints on deviations from the standard behavior of the gravitational interaction at short distances predicted by large extra-dimensional models. We compute explicitly, in the thick-brane scenario, the corrections to the neutron–nucleus scattering length arising from the influence of hidden dimensions. The experimental data allow us to place empirical bounds on the free parameters of the extra-dimensional model, expressed as a function of the nuclear scattering length. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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