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Aneta Wojnar

Publications and source records attributed to Aneta Wojnar.

At least 37 records · Page 2Linked to original sources
arXiv2023

Cosmological constraints of Palatini $f(\mathcal{R})$ gravity

In this study, we investigate a Palatini $f(R)$ gravity model featuring a quadratic term correction, aligning it with the most recent expansion rate data, with a particular focus on the latest SNIa and BAO data. Our analysis employs CC data as the fundamental dataset, complemented by contributions from the SN sample and a combination of non-overlapping transversal BAO datasets. We conduct a comprehensive MCMC analysis for each data set combination, yielding constraints on all cosmological parameters within the model. Additionally, we incorporate the latest Hubble constant value from the SH0ES Team. Finally, we present a statistical comparison between the Palatini quadratic model and $Λ$CDM using the AIC and BIC metrics, ultimately obtaining the constraint $|α| \leq 10^{49}\,\text{m}^2$. We also stress the significance of studying stellar and substellar objects for obtaining more precise constraints on modified gravity compared to those derived from cosmological observations.

gr-qc↗
arXiv2023

Fermi equation of state with finite temperature corrections in quantum space-times approach: Snyder model vs GUP case

We investigate the impact of the deformed phase space associated with the quantum Snyder space on microphysical systems. The general Fermi-Dirac equation of state and specific corrections to it are derived. We put emphasis on non-relativistic degenerate Fermi gas as well as on the temperature-finite corrections to it. Considering the most general one-parameter family of deformed phase spaces associated with the Snyder model allows us to study whether the modifications arising in physical effects depend on the choice of realization. It turns out that we can distinguish three different cases with radically different physical consequences.

gr-qc↗
arXiv2023

Planetary seismology as a test of modified gravity proposals

We demonstrate that it is possible to test models of gravity, such as Palatini $f(R)$ and Eddington-inspired Born-Infeld models, using seismic data from Earth. By incorporating additional limitations on Earth's moment of inertia and mass given from observational data, the models' parameters can be restricted to a $2σ$ level of accuracy. Our novel tool provides that the parameter $β$ parametrizing the quadratic curvature term in the gravitational Lagrangian of Palatini $f(R)$ gravity is constrained to $β\lesssim 10^9 \text{m}^2$ while the Eddington-inspired Born-Infeld gravity parameter $ε$ is restricted to $ε\lesssim 4\cdot 10^9 \text{m}^2$. We also discuss further enhancements to the proposed method, aimed at imposing even more stringent constraints on modified gravity proposals.

gr-qc↗
arXiv2023

Earthquakes as probing tools for gravity theories

We propose a novel method for testing gravity models using seismic data from Earth. By imposing observational constraints on Earth's moment of inertia and mass, we rigorously limit the gravitational models' parameters within a $2σ$ accuracy. Our method constrains the parameters governing additional terms to the General Relativity Lagrangian to the following ranges: $-2\times10^9\lesssimβ\lesssim 10^9 \text{m}^2$ for Palatini $f(R)$ gravity, $-8\times10^9\lesssimε\lesssim 4\times 10^9 \text{m}^2$ for Eddington-inspired Born-Infeld gravity, and $-10^{-3}\lesssimΥ\lesssim10^{-3}$ 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.

gr-qc↗
arXiv2023

Palatini $f(R)$ gravity tests in the weak field limit: Solar System, seismology and galaxies

Palatini $f(R)$ gravity is probably the simplest extension of general relativity (GR) and the simplest realization of a metric-affine theory. It has the same number of degrees of freedom as GR and, in vacuum, it is straightforwardly mapped into GR with a cosmological constant. The mapping between GR and Palatini $f(R)$ inside matter is possible but at the expense of reinterpreting the meaning of the matter fields. The physical meaning and consequences of such mapping will depend on the physical context. Here we consider three such cases within the weak field limit: Solar System dynamics, planetary internal dynamics (seismology), and galaxies. After revising our previous results on the Solar System and Earth's seismology, we consider here the possibility of $f(R)$ Palatini as a dark matter candidate. For any $f(R)$ that admits a polynomial approximation in the weak field limit, we show here, using SPARC data and a recent method that we proposed, that the theory cannot be used to replace dark matter in galaxies. We also show that the same result applies to the Eddington-inspired Born-Infeld gravity. Differently from the metric $f(R)$ case, the rotation curve data are sufficient for this conclusion. This result does not exclude a combination of modified gravity and dark matter.

gr-qc↗
arXiv2023

Early evolution of fully convective stars in scalar-tensor gravity

In this work, the early evolution of low-mass fully convective stars is studied in the context of DHOST (degenerate higher order scalar-tensor) theories of gravity. Although it is known that the hydrostatic equilibrium equation is modified for scalar-tensor gravity, the consequent modifications to the early evolution phases of a star were not explored in this framework. With this in mind, we consider three evolutionary phases - contraction to the main sequence, lithium burning and entrance to the main sequence - and investigate how each of these phases is affected by the theory's parameter. Taking these effects into account, we are able to show, among other things, that the Hayashi tracks are shifted and the star's age is considerably modified.

gr-qc↗
arXiv2023

Modified Gravity and Cosmology: An Update by the CANTATA Network

General Relativity and the $Λ$CDM framework are currently the standard lore and constitute the concordance paradigm. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology the last two decades, offer the motivation and lead a large amount of research to be devoted in constructing various extensions and modifications. All extended theories and scenarios are first examined under the light of theoretical consistency, and then are applied to various geometrical backgrounds, such as the cosmological and the spherical symmetric ones. Their predictions at both the background and perturbation levels, and concerning cosmology at early, intermediate and late times, are then confronted with the huge amount of observational data that astrophysics and cosmology are able to offer recently. Theories, scenarios and models that successfully and efficiently pass the above steps are classified as viable and are candidates for the description of Nature. This work is a Review of the recent developments in the fields of gravity and cosmology, presenting the state of the art, high-lighting the open problems, and outlining the directions of future research. Its realization was performed in the framework of the COST European Action ``Cosmology and Astrophysics Network for Theoretical Advances and Training Actions''.

gr-qc↗
arXiv2023

Normalized additional velocity distribution: testing the radial profile of dark matter halos and MOND

We propose a complementary and fast approach to study galaxy rotation curves directly from the sample data, instead of individual fits. With this approach, some relevant tests can be done analytically. It is based on a dimensionless difference between the observational rotation curve and the expected one from the baryonic matter ($δV^2$) as a function of the normalized radius $r_n$ (i.e., for all galaxies, $0 < r_n < 1$). Using 153 galaxies from the SPARC galaxy sample, we find the observational distribution of $δV^2$. Considering radii with $0.2 < r_n < 0.9$, most of the SPARC data are close to the curve $δV^2 = r_n^{0.42}$, and about $95\%$ of the SPARC data is between the curves $δV^2 = r_n^{2.2}$ and $δV^2 = 2 r_n^{0.38} - r_n^{1.9} $. We consider three well known dark matter halo models (NFW, Burkert and DC14), a simple dark matter rotation curve profile for the purpose of model comparison (Arctan$_α$) and one modified gravity model without dark matter (MOND). By comparing the observational data distribution with the model-inferred data, we confirm that the NFW halo lacks the necessary diversity to reproduce several observed rotation curves, while Burkert and DC14 models have better concordance with observational data. The lowest $δV^2$ curves that can be found from NFW are linear on the normalized radius (i.e., $δV^2_{NFW} = r_n$), while for Burkert $δV^2_{Bur} = r_n^2$ (this result is independent of the halo density parameter, i.e., $ρ_{c}$ or $ρ_{s}$). MOND only covers the very central region of the observed distribution, hence it also lacks the necessary diversity, which in turn is related to larger $χ^2$ values. In a second paper, the method will be extended to consider other classes of modified gravity models.

astro-ph.GA↗
arXiv2023

Metric-affine effects in crystallization processes of white dwarfs

We analyze the effects of modified gravity on specific heats of electrons and ions, Debye temperature, crystallization process, and cooling mechanism in white dwarfs. We derive the Lane-Emden-Chandrasekhar 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.

gr-qc↗
arXiv2023

Fermi gas and modified gravity

We derive the equations of state of Fermi gas by maximizing the Fermi-Dirac entropy in modified gravity in relativistic and non-relativistic case. It will be demonstrated that the microphysics must depend on a given theory of gravity in order to consistently describe a physical system at a statistical equilibrium state.

gr-qc↗
arXiv2022

Cooling Process of White Dwarf Stars in Palatini $f(R)$ Gravity

A simple cooling model of white dwarf stars is re-analyzed in Palatini $f(R)$ gravity. Modified gravity affects the white dwarf structures and consequently their ages. We find that the resulting super-Chandrasekhar white dwarfs need more time to cool down than sub-Chandrasekhar ones, or when compared to the Newtonian models.

gr-qc↗
arXiv2022

Non-homogeneous exoplanets in metric-affine gravity

The improved description of the planets' interior is provided. We examine the modified gravity effects on the Earth-like planets composed of the iron core and silicate mantle. We confirm that the mass-radius relations, as well as density profiles, differ with respect to the commonly adopted Newtonian models.

gr-qc↗
arXiv2022

Stellar and substellar objects in modified gravity

The last findings on stellar and substellar objects in modified gravity are presented, allowing a reader to quickly jump into this topic. Early stellar evolution of low-mass stars, cooling models of brown dwarfs and giant gaseous exoplanets as well as internal structure of terrestrial planets are discussed. Moreover, possible test of models of gravity with the use of the discussed objects are proposed.

gr-qc↗
arXiv2022

Giant planet formation in Palatini gravity

Some parts of the accretion model of the jovian planets' formation are studied in the context of Palatini gravity. We mainly focus on the critical core mass, that is, a mass for which there is no hydrostatic equilibrium solution for the planet's envelope, which is a starting point of the runaway accretion. We also discuss the conditions needed to be satisfied by a planet such that it can posses a massive gaseous envelope around a solid core.

gr-qc↗
arXiv2021

Stability criterion for white dwarfs in Palatini $f(R)$ gravity

Recent observations of several peculiar over- and under-luminous type Ia supernovae infer indirect evidence for the violation of the Chandrasekhar mass-limit by suggesting the existence of super- and sub-Chandrasekhar limiting mass white dwarfs. In an attempt to explain these phenomena in the context of general relativistic extensions, we study these objects in Palatini $f(R)$ gravity. We obtain the super- and sub-Chandrasekhar limiting masses as well as the dynamical instability criteria for white dwarfs in the given gravitational theory. We further demonstrate that the conventional positivity condition $\partial{M}/\partial{ρ_\text{c}}>0$ with $M$ being the WD's mass with central density $ρ_\text{c}$, is also a valid criterion for stability in Palatini gravity.

gr-qc↗
arXiv2021

Pre-main sequence evolution of low-mass stars in Eddington-inspired Born-Infeld gravity

We study three aspects of the early-evolutionary phases in low-mass stars within Eddington-inspired Born-Infeld (EiBI) gravity, a viable extension of General Relativity. These aspects are concerned with the Hayashi tracks (i.e. the effective temperature-luminosity relation); the minimum mass required to belong to the main sequence; and the maximum mass allowed for a fully convective star within the main sequence. In all cases we find a dependence of these quantities not only on the theory's parameter, but also on the star's central density, a feature previously found in Palatini $f(R)$ gravity. Using this, we investigate the evolution of these quantities with the (sign of the) EiBI parameter, finding a shift in the Hayashi tracks in opposite directions in the positive/negative branches of it, and an increase (decrease) for positive (negative) parameter in the two masses above. We use these results to ellaborate on the chances to seek for traces of new physics in low-mass stars within this theory.

gr-qc↗