Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama
Summary: This paper introduces a new cosmological framework integrating dark matter into a minimally modified gravity model, maintaining the same number of gravitational degrees of freedom through a series of transformations. The framework includes two time-dependent free functions to achieve desired evolutions of Hubble expansion rate and effective gravitational constant for dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Yuewei Wen, Eva Nesbit, Dragan Huterer, Scott Watson
Summary: Standard cosmological data analyses can't easily determine the presence of modified gravity. This study presents a quantitative mapping showing how modified gravity models appear within standard analyses, reporting specific biases in standard-parameter spaces. The implications for measurements of mass fluctuations are also discussed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
A. Arbey, J-F Coupechoux
Summary: This paper explores the possibility of a scalar field replacing dark matter, dark energy, and inflation by introducing a non-minimal coupling to gravity, a Mexican hat potential, and spontaneous symmetry breaking. The scalar field behaves like a dark fluid after inflation, mimicking the properties of both dark energy and dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Yuri Shtanov
Summary: This study gives an overview of the possibility of the scalaron in f (R) gravity theory constituting dark matter, and raises the issues of initial conditions and primordial spatial inhomogeneity, as well as proposes solutions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Alexander B. Balakin, Alexei S. Ilin
Summary: We propose a new self-consistent model that couples cosmic dark energy and dark matter using the rheological approach. This model represents the equations of state as integral operators of the Volterra type. We classify the exact solutions of the model based on the roots of the characteristic polynomial. The pressure, energy density, Hubble function, and acceleration parameter of dark energy and dark matter are expressed explicitly as functions of the dimensionless scale factor. We discuss two intriguing cosmological solutions that describe superexponential expansion and symmetric bounce, as well as new solutions corresponding to quasiperiodic behavior.
Article
Astronomy & Astrophysics
Alexander Ganz
Summary: Minimally modified gravity models use auxiliary constraints to maintain a dynamic cosmological background, with results of linear perturbations being insensitive to constraint details, leading to a modified effective gravitational constant or a non-zero dust sound speed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Nuclear
Hua Chen, Taishi Katsuragawa, Shinya Matsuzaki
Summary: This paper investigates R-2 corrected dark energy models in F(R) gravity, providing a unified interpretation of the cosmic history by exploring the universal features of scalaron dynamics and the chameleon mechanism. The study shows that catastrophic consequences claimed in the literature do not apply to this class of models, due to the presence of a large scale hierarchy between R-2 correction and dark energy. The prospects for the inflationary and dark energy epochs differ from the standard scenario due to the chameleon mechanism.
Article
Astronomy & Astrophysics
Tilek Zhumabek, Mikhail Denissenya, Eric V. Linder
Summary: This study explores the connection between early universe inflation and present-day dark energy through quintessential inflation without a cosmological constant. The researchers demonstrate a robust relationship between the dark energy equation of state parameter and the primordial tensor to scalar ratio for a wide range of initial conditions. The study suggests that upcoming cosmic microwave background and galaxy redshift surveys can test the consistency condition.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
Mikhail Shaposhnikov, Andrey Shkerin, Inar Timiryasov, Sebastian Zell
Summary: This passage discusses a novel mechanism for producing singlet fermions in the early Universe through gravity-induced interactions. These fermions can act as dark matter particles and are applicable to a wide range of dark matter particle masses. The potential observational consequences of producing keV-scale dark matter in this way, particularly for right-handed neutrinos, are also explored. The authors suggest that determining the momentum distribution of primordial dark matter may shed light on gravity-induced fermionic interactions.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Chunshan Lin
Summary: This study presents a general covariant local field theory of the holographic dark energy model, showing that the low energy effective theory is the massive gravity theory with a scalar graviton having strong coupling at certain energy scale. The UV-IR correspondence in this model stems from the breakdown of the effective field theory at the energy scale.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Alexandros Karam, Martti Raidal, Eemeli Tomberg
Summary: The study focuses on preheating in plateau inflation in a scenario similar to Higgs inflation, revealing that the oscillating inflaton field repeatedly returns to the plateau, leading to tachyonic production of inflaton particles. Moreover, it is demonstrated that a minimally coupled spectator scalar field can be more efficiently produced through a similar mechanism. The mechanism is solely gravitational and the scalar field mass can be as high as 10^13 GeV, making it a candidate for superheavy dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Ahmad Sheykhi, Maral Sahebi Hamedan
Summary: The thermodynamics-gravity conjecture suggests a strong connection between the gravitational field equations and the first law of thermodynamics, meaning any changes in entropy expression directly impact the field equations. By considering the modified Barrow entropy associated with the apparent horizon, the Friedmann equations are altered as well. This paper explores the implications of this modification on the holographic dark energy (HDE) model, highlighting changes in energy density and the Friedmann equations. The study also investigates the cosmological consequences of using the Hubble horizon and future event horizon as infrared cutoffs, including interactions between dark matter (DM) and dark energy (DE), and the impact of the Barrow exponent on the cosmological behavior of HDE, such as crossing the phantom line and shifting the universe phase transition time.
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, Diego Saez-Chillon Gomez
Summary: In the era of precision cosmology, the Hubble tension problem arises from precise measurements of the Hubble constant that differ significantly due to different observational data. To solve this discrepancy, various solutions have been proposed, including considering systematic errors on the observational data and theoretical proposals involving an early dark energy that affects the universe expansion. In this paper, a model of varying cosmological constant in Einstein-Gauss-Bonnet gravity framework is introduced, which successfully explains the inflationary era, dark energy epoch, and the discrepancy in the predictions of the Hubble constant.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Mohammad Ali Gorji, Hayato Motohashi, Shinji Mukohyama
Summary: In the context of scalar-tensor theories, stealth de Sitter solutions face issues of infinite strong coupling or gradient instability, which can be resolved by introducing a controlled detuning mechanism known as scordatura. This mechanism not only resolves the mentioned issues, but also ensures a well-defined quasi-static limit.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Particles & Fields
Kazuharu Bamba, Z. Yousaf, M. Z. Bhatti, R. Nazer, Yuki Hashimoto
Summary: This paper explores the collapsing dynamics of relativistic fluid in f (R) gravity in a detailed and systematic manner. Exact solutions for both dissipative and non-dissipative systems are found under the conditions of quasi-homologous and diminishing complexity factor. The astrophysical applications of these solutions are discussed, and it is shown that the previous solutions of collapsing fluid in general relativity can be retrieved when f (R) = R.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Mathematical
Aneta Wojnar
Summary: Modified gravity framework may provide alternative explanations to white dwarfs' cooling processes, age determination, and Chandrasekhar mass limits. Additionally, the Chandrasekhar limit has been obtained from Palatini f(Script capital R) gravity introduced by a simple Lane-Emden model.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Article
Astronomy & Astrophysics
Aleksander Kozak, Aneta Wojnar
Summary: Using a semiempirical approach, this study demonstrates that modified gravity has an impact on the internal properties of terrestrial planets, including their core, mantle, and core-mantle boundary. These findings are also applied to modeling a two-layer exoplanet under Palatini f(R) gravity.
Article
Physics, Mathematical
Aleksander Kozak, Aneta Wojnar
Summary: This article provides an improved description of the planets' interior and examines the effects of modified gravity on Earth-like planets composed of iron core and silicate mantle.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
Surajit Kalita, Lupamudra Sarmah, Aneta Wojnar
Summary: In this study, a simple cooling model of white dwarf stars is analyzed in Palatini f(R) gravity. It is found that modified gravity affects the structures and ages of white dwarfs, resulting in super-Chandrasekhar white dwarfs requiring more time to cool down compared to sub-Chandrasekhar ones or Newtonian models.
Article
Physics, Mathematical
Alejandro Hernandez-Arboleda, Davi C. Rodrigues, Junior D. Toniato, Aneta Wojnar
Summary: Palatini f(R) gravity is a simple extension of general relativity that can be mapped into GR with a cosmological constant. By reinterpreting the meaning of matter fields, GR and Palatini f(R) can be mapped within matter. In the weak field limit, we consider three cases and find that Palatini f(R) cannot replace dark matter in galaxies.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Particles & Fields
Debora Aguiar Gomes, Aneta Wojnar
Summary: In this work, the early evolution of low-mass fully convective stars is studied in the context of DHOST theories of gravity, specifically focusing on the modifications to the hydrostatic equilibrium equation and their effects on different evolutionary phases. The Hayashi tracks are found to be shifted and the star's age is significantly modified under the influence of the theory's parameter.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Aneta Wojnar
Summary: The equations of state for Fermi gas in modified gravity are derived by maximizing the Fermi-Dirac entropy in both relativistic and nonrelativistic cases. It is shown that the microphysics of a physical system at a statistical state must depend on a specific theory of gravity in order to be consistently described.
Article
Astronomy & Astrophysics
Surajit Kalita, Lupamudra Sarmah, Aneta Wojnar
Summary: We analyze the effects of modified gravity on specific heats, Debye temperature, crystallization process, and cooling mechanism in white dwarfs. We derive the Lane-Emden-Chandra-sekhar equation and relate it to the cooling process equations for Palatini f(R) gravity. Moreover, for the first time in the literature, we show that the gravity model plays a crucial role not only in the mass and size of the white dwarf but also affects their internal properties. We further demonstrate that modified gravity can decrease the cooling age significantly.
Article
Physics, Particles & Fields
Anna Pachol, Aneta Wojnar
Summary: We investigate the application of incorporating corrections from the Snyder model and the Generalized Uncertainty Principle into the equation of state to describe the behavior of matter in a low-mass star. The resulting equations exhibit striking similarities to those arising from modified Einstein gravity theories. By modeling matter with realism, we are able to effectively constrain the theory parameters beyond existing astrophysical bounds.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Aleksander Kozak, Kart Soieva, Aneta Wojnar
Summary: The cooling processes of brown dwarf stars and giant planets are examined within the framework of degenerate higher-order scalar-tensor theories. The findings confirm previous studies that modified gravity has the most pronounced effect on the age of substellar objects.
Article
Astronomy & Astrophysics
Aneta Wojnar
Summary: The study focuses on the critical core mass and the conditions for a planet to possess a massive gaseous envelope around a solid core during early planetary formation.
Article
Physics, Particles & Fields
Merce Guerrero, Diego Rubiera-Garcia, Aneta Wojnar
Summary: This study investigates three aspects of the early-evolutionary phases in low-mass stars within Eddington-inspired Born-Infeld (EiBI) gravity, including the Hayashi tracks, the minimum mass required for the main sequence, and the maximum mass for a fully convective star. The results show a dependence of these quantities on both the EiBI parameter and the star's central density.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
A. Borowiec, A. Kozak
Summary: This paper revisits the general minisuperspace formalism for scalar tensor Friedmann-Lemake-RobertsonWalker cosmological models in an arbitrary frame. It discusses the imposition of Cauchy data on the corresponding dynamical system and extends the study to an arbitrary frame with nonminimal coupling between matter and gravity. The paper explores the gauge freedom associated with the choice of lapse function and shows the relation between particular isothermal minisuperspace coordinates and equivalent classes in the Einstein frame.
Article
Astronomy & Astrophysics
Lupamudra Sarmah, Surajit Kalita, Aneta Wojnar
Summary: Recent observations suggest the violation of Chandrasekhar mass limit in supernovae and the existence of white dwarfs with super- and sub-Chandrasekhar limiting masses. In this study, we investigate these objects using Palatini f(R) gravity in the context of general relativistic extensions. We determine the limiting masses and dynamical instability criteria for white dwarfs in this gravitational theory. Furthermore, we demonstrate that the conventional positivity condition remains valid for stability in Palatini gravity.
Article
Astronomy & Astrophysics
Aneta Wojnar
Summary: Palatini f((R) over bar) gravity has been shown to impact certain parts of substellar evolution, such as fragmentation of a gaseous cloud and cooling of Jupiter-like planets. Simple models describing these processes demonstrate differences in opacity mass limit and cooling time of jovian planets in modified gravity.
