arXiv subjects

Aneta Wojnar

Publications and source records attributed to Aneta Wojnar.

At least 19 recordsLinked to original sources

arXiv2026

Temperature effects on white dwarfs in modified gravity

In this article we analyze the effects of a finite temperature equation of state on the equilibrium structure of white dwarfs in massive Brans-Dicke theory as well as the symmetron and dilaton screening mechanisms. We compute and present the numerically obtained mass-radius relation, effective gravitational constant as well as radial profiles of the scalar field, pressure and metric within the star. We show that assuming a non-zero temperature effectively results in a larger radius while leaving the total mass of the star essentially unchanged, and discuss the interplay between the effective gravitational constant, central density, and radius of the star.

gr-qc↗

arXiv2026

Einstein crystals in Snyder and Snyder-de Sitter noncommutative backgrounds

We investigate the behavior of Einstein crystals in noncommutative backgrounds described by the Snyder and Snyder-de Sitter models. Possible novel effects, which may arise in realistic systems such as diamond crystals, are analyzed within a thermodynamical framework. We show that noncommutativity influences the key thermodynamic quantities, including internal energy and specific heat. These corrections can be directly related to modifications of the underlying uncertainty relations, of the generalized uncertainty principle (GUP) and generalized extended uncertainty principle (GEUP) types.

gr-qc↗

arXiv2026

When waves meet rays: Seismic vibrations and cosmic showers to test gravity

We propose a novel laboratory test of gravity combining seismic-wave measurements with cosmic-ray muon detections. Quantum-gravity corrections to the anharmonic Debye model are derived, yielding a modified bulk modulus that encodes deviations from standard gravity. The usual dependence on density, a dominant source of uncertainty, is removed via muon tomography and seismic velocities measurement. We show that this setup can constrain gravity parameters at a level comparable to current laboratory experiments. Prospects for further improvements are briefly discussed.

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arXiv2025

The effects of strong gravity on the dispersion relation of massive particles in the Kaluza-Klein theory

We derive a modified dispersion relation for massive particles within the frameworks of five-dimensional Kaluza-Klein theory and general relativity, taking into account strong gravitational effects. The resulting effective mass depends on the curvature of the underlying phase space. Notably, in regions with strong gravitational fields, the effective mass may become imaginary, implying the possibility of particle decay induced by spacetime curvature.

gr-qc↗

arXiv2024

Testing gravity with the latent heat of neutron star matter

The Seidov limit is a bound on the maximum latent heat that a presumed first-order phase transition of neutron-star matter can have before its excess energy density, not compensated by additional pressure, results in gravitational collapse. Because latent heat forces an apparent nonanalytic behaviour in plots correlating physical quantities (kinks in two-dimensional, ridges in three-dimensional ones), it can be constrained by data. As the onset of collapse depends on the intensity of gravity, testing for sudden derivative changes and, if they are large, breaching the Seidov limit would reward with two successive discoveries: such a phase transition (which could stem from hadron matter but also from a gravitational phase transition), and a modification of General Relativity (thus breaking the matter/gravity degeneracy). We illustrate the point with $f(R)=R+\alpha R^2$ metric gravity.

gr-qc↗

arXiv2024

Foliation-generating observers under Lorentz transformations

In this work, we revise the concept of foliation and related aspects that are crucial when formulating the Hamiltonian evolution for various theories beyond General Relativity. In particular, we show the relation between the kinematic characteristics of timelike congruences (observers) and the existence of foliations orthogonal to them. We then explore how local Lorentz transformations acting on observers affect the existence of transversal foliations, provide examples, and discuss the implications of these results for the $3+1$ formulation of tetrad modified theories of gravity.

gr-qc↗

arXiv2024

Crystallized white dwarf stars in scalar-tensor gravity

We study the effects of massive scalar-tensor theories on the internal properties, crystallization, and cooling process of white dwarf stars that might potentially solve observational tensions. We show that these modified gravity theories alter the inner structure of the star leading to sub-Chandrasekhar mass white dwarfs. This further results in a modification of Debye temperature, ion and electron specific heats. Finally, we find that the cooling process is significantly shortened in scalar-tensor theories leading to reduced cooling ages.

gr-qc↗

arXiv2024

Bose and Fermi gases in metric-affine gravity and linear Generalized Uncertainty Principle

We examine the relationship between Palatini-like theories of gravity and models incorporating linear generalized uncertainty principles. Additionally, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, Bose gases such as phonons and photons, as well as Bose-Einstein condensates and liquid helium.

gr-qc↗

arXiv2024

Twin Stars in General Relativity and Extended Theories of Gravity

We explore gravity-independent equations of state for neutron stars, particularly focusing on twin stars. Examining four categories, we emphasize their behavior in both General Relativity and Palatini gravity. Additionally, we discuss a subcategory of type I, which, in the context of General Relativity, does not exhibit twin star phenomena, yet demonstrates this phenomenon in modified gravity. Furthermore, we briefly address challenges associated with the negative trace of the energy-momentum tensor, prevalent in both theories.

gr-qc↗

arXiv2024

Effects of modified gravity on microscopic properties and cooling timescale of white dwarfs

There are currently two open questions in white dwarf physics: why are massive dwarfs observed less often in astronomical surveys, and why have not any super-Chandrasekhar white dwarfs been found despite the discovery of more than a dozen peculiar, overly-luminous type Ia supernovae in about a couple of decades? According to different research, magnetic fields appear to somewhat resolve these issues, but stability remains a concern. For the first time, we investigate how modified gravity affects the specific heat of electrons and ions, the crystallization process, and the cooling mechanism in white dwarfs. We demonstrate it for the Ricci-based gravity. We show that massive white dwarfs fade faster and conclude that it could be a physical reason, apart from the presence of high magnetic fields, both for finding fewer massive white dwarfs and the lack of direct detection of super-Chandrasekhar white dwarfs.

astro-ph.SR↗

arXiv2024

A covariant tapestry of linear GUP, metric-affine gravity, their Poincar\'e algebra and entropy bound

Motivated by the potential connection between metric-affine gravity and linear Generalized Uncertainty Principle (GUP) in the phase space, we develop a covariant form of linear GUP and an associated modified Poincar\'e algebra, which exhibits distinctive behavior, nearing nullity at the minimal length scale proposed by linear GUP. We use 3-torus geometry to visually represent linear GUP within a covariant framework. The 3-torus area provides an exact geometric representation of Bekenstein's universal bound. We depart from Bousso's approach, which adapts Bekenstein's bound by substituting the Schwarzschild radius ($r_s$) with the radius ($R$) of the smallest sphere enclosing the physical system, thereby basing the covariant entropy bound on the sphere's area. Instead, our revised covariant entropy bound is described by the area of a 3-torus, determined by both the inner radius $r_s$ and outer radius $R$ where $r_s\leq R $ due to gravitational stability. This approach results in a more precise geometric representation of Bekenstein's bound, notably for larger systems where Bousso's bound is typically much larger than Bekensetin's universal bound. Furthermore, we derive an equation that turns the standard uncertainty inequality into an equation when considering the contribution of the 3-torus covariant entropy bound, suggesting a new avenue of quantum gravity.

gr-qc↗

arXiv2024

Bose-Einstein Condensate and Liquid Helium He$^4$: Implications of GUP and Modified Gravity Correspondence

Utilizing the recently established connection between Palatini-like gravity and linear Generalized Uncertainty Principle (GUP) models, we have formulated an approach that facilitates the examination of Bose gases. Our primary focus is on the ideal Bose-Einstein condensate and liquid helium, chosen as illustrative examples to underscore the feasibility of tabletop experiments in assessing gravity models. The non-interacting Bose-Einstein condensate imposes constraints on linear GUP and Palatini $f(R)$ gravity (Eddington-inspired Born-Infeld gravity) within the ranges of $-10^{12}\lesssim\sigma\lesssim 3\times 10^{24}{\text{ s}}/{\text{kg m}}$ and $-10^{-1}\lesssim\bar\beta\lesssim 10^{11} \text{ m}^2$ ($-4\times10^{-1}\lesssim\epsilon\lesssim 4\times 10^{11} \text{ m}^2$), respectively. In contrast, the properties of liquid helium suggest more realistic bounds, specifically $-10^{23}\lesssim\sigma\lesssim 10^{23}{\text{ s}}/{\text{kg m}}$ and $-10^{9}\lesssim\bar\beta\lesssim 10^{9} \text{ m}^2$. Additionally, we argue that the newly developed method employing Earth seismic waves provides improved constraints for quantum and modified gravity by approximately one order of magnitude.

gr-qc↗

arXiv2023

Propagation and lensing of gravitational waves in Palatini $f(\hat R)$ gravity

Accelerated expansion of the Universe prompted searches of modified gravity theory beyond general relativity, instead of adding a mysterious dark energy component with exotic physical properties. One such alternative gravity approach is metric-affine Palatini $f(\hat{R})$ theory. By now routine gravitational wave detections have opened a promising avenue of searching for modified gravity effects. Future expected cases of strong lensing of gravitational waves will enhance this opportunity further. In this paper, we present a systematic study of the propagation and gravitational lensing of gravitational waves in Palatini $f(\hat R)$ gravity and compare it with general relativity. Using the WKB approximation we explore the geometric-optical limit of lensing and derive the corrections to the measured luminosity distance of the gravitational source. In addition, we study the lensing by the Singular Isothermal Sphere lens model and show that Palatini $f(\hat{R})$ modifies the lensing potential and hence the deflection angle. Then we show that the lens model and chosen theory of gravity influences the rotation of the gravitational wave polarization plane through the deflection angle. To be more specific we discuss the $f(\hat R)=\hat R+\alpha \hat R^2$ gravity theory and find that the modifications comparing to general relativity are negligible if the upper bound of $\alpha \sim 10^{9} \, $m$^2$ suggested in the literature is adopted. However, this bound is not firmly established and can be updated in the future. Therefore, the results we obtained could be valuable for further metric-affine gravity vs. general relativity tests involving lensing of gravitational waves and comparison of luminosity distances measured from electromagnetic and gravitational wave sources.

gr-qc↗

arXiv2023

Introduction to stellar and substellar physics in modified gravity

We discuss the standard Lane-Emden formalism as well as the one related to the slowly rotating objects. It is preceded by a brief introduction of different forms of the polytropic equation of state. This allows to study a wide class of astrophysical objects in the framework of a given theory of gravity, as demonstrated in a few examples. We will discuss light elements burning processes and cooling models in stars and substellar objects with the use of the Lane-Emden formalism.

gr-qc↗

arXiv2023

Unveiling Phase Space Modifications: A Clash of Modified Gravity and the Generalized Uncertainty Principle

This study explores the link between Modified Gravity and modifications of phase space volume. Analyzing Fermi gas modifications {in the non-relativistic limit of the} Ricci-based gravities, we derive a generalized partition function in the grand-canonical ensemble, connecting Modified Gravity models with the Generalized Uncertainty Principle. Using this correspondence, we also establish bounds on the linear Generalized Uncertainty Principle: $-6\times10^{22}\lesssim\sigma\lesssim 3\times 10^{22}{\text{ s}}/{\text{kg m}}$, as well as lower bounds for Palatini $f(R)$ gravity $\beta > -7.51587\times 10^7 \text{ m}^2$ and Eddington-inspired Born-Infeld gravity $\epsilon > -1.88\times 10^7 \text{ m}^2$, ensuring microscopic stability. This connection also facilitates testing gravity proposals through tabletop experiments.

gr-qc↗

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 $\Lambda$CDM using the AIC and BIC metrics, ultimately obtaining the constraint $|\alpha| \leq 10^{49}\,\text{m}^2$. 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

Refining Bounds for Snyder and GUP Models through Seismic Wave Analysis

This study investigates possibility of placing bounds on the parameters, arising from the non-commutative Snyder space-time model and Generalized Uncertainty Principle (GUP) approach, by utilizing seismic data. We investigate the dependence of constraints on the type of realization used for the quantum phase space. Results indicate improved bounds compared to prior studies, with the model parameter $\beta_0$ constrained to be less than $5.2\times 10^{44}$ for certain choice of realizations. This approach demonstrates the potential for using Earth's empirical data to refine constraints on GUP parameters.

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 $2\sigma$ accuracy. Our method constrains the parameters governing additional terms to the General Relativity Lagrangian to the following ranges: $-2\times10^9\lesssim\beta\lesssim 10^9 \text{m}^2$ for Palatini $f(R)$ gravity, $-8\times10^9\lesssim\epsilon\lesssim 4\times 10^9 \text{m}^2$ for Eddington-inspired Born-Infeld gravity, and $-10^{-3}\lesssim\Upsilon\lesssim10^{-3}$ 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↗