Thermodynamical aspects of black holes in modified gravity

Modified Cosmology Models from Thermodynamical Approach

We apply the first law of thermodynamics to the apparent horizon of the universe with the power-law corrected and non-extensive Tsallis entropies rather than the Bekenstein-Hawking one. We examine the cosmological properties in the two entropy models by using the CosmoMC package. In particular, the first numerical study for the cosmological observables with the power-law corrected entropy is performed. We also show that the neutrino mass sum has a non-zero central value with a relaxed upper bound in the Tsallis entropy model comparing with that in the $Λ$CDM one.

Thermodynamics of the Variable Modified Chaplygin gas

A cosmological model with a new variant of Chaplygin gas obeying an equation of state(EoS), $P = Aρ- \frac{B}{ρ^α}$ where $B= B_{0}a^{n}$ is investigated in the context of its thermodynamical behaviour. Here $B_{0}$ and $n$ are constants and $a$ is the scale factor. We show that the equation of state of this `Variable Modified Chaplygin gas' (VMCG) can describe the current accelerated expansion of the universe. Following standard thermodynamical criteria we mainly discuss the classical thermodynamical stability of the model and find that the new parameter, $n$ introduced in VMCG plays a crucia…

Chemistry of Chern-Simons Supergravity: reduction to a BPS kink, oxidation to M-theory and thermodynamical aspects

We construct a supersymmetric extension of the two dimensional Kaluza-Klein-reduced gravitational Chern-Simons term, and globally study its solutions, labelled by mass and U(1) charge c. The kink solution is BPS, and in an appropriate conformal frame all solutions asymptotically approach AdS. The thermodynamics of the Hawking effect yields interesting behavior for the specific heat and hints at a Hawking-Page-like transition at T_{critical} \sim c^{3/2}. We address implications for higher dimensions ("oxidation"), in particular D=3,4 and 11, and comment briefly on AdS/CFT aspects of the kink.

Quasinormal modes and thermodynamical aspects of the 3D Lifshitz black hole

We consider scalar and spinorial perturbations on a background described by a $z=3$ three-dimensional Lifshitz black hole. We obtained the corresponding quasinormal modes which perfectly agree with the analytical result for the quasinormal frequency in the scalar case. The numerical results for the spinorial perturbations reinforce our conclusion on the stability of the model under these perturbations. We also calculate the area spectrum, which prove to be equally spaced, as an application of our results.

广义第二定律与$f(Q,\mathcal{T})$引力的热力学方面

Generalized Second Law and Thermodynamical Aspects of $f(Q,\mathcal{T})$ Gravity

本文研究了$f(Q,\mathcal{T})$引力的热力学特性，通过在平坦FLRW宇宙的视界上建立热力学第一定律和广义第二定律，分析了不同$f(Q,\mathcal{T})$模型下熵变化率及广义第二定律的有效条件。

Horizon Entropy in Modified Gravity

We present an observation about the proposal that four-dimensional modification of general relativity may explain the observed cosmic acceleration today. Assuming that the thermodynamical nature of gravity theory continues to hold in modified gravity theories, we derive the modified horizon entropy formula from the modified Friedmann equation. We argue that our results imply that there are conceptual problems in some models of four-dimensional modification of general relativity.

修正引力中的黑洞热力学

Black hole thermodynamics in modified gravity

本文在修正爱因斯坦引力框架下探索黑洞热力学，发现即使对爱因斯坦引力的微小修正也会改变黑洞的热力学性质。

某些宇宙学模型的热力学方面

Thermodynamical Aspects of Some Cosmological Models

本文基于 FRW 度规，对解释晚期宇宙加速的 quintessence、Brans-Dicke 及暗能量等模型进行了热力学分析，评估了其广义第二定律兼容性与热力学稳定性。

Thermodynamical Properties and Quasi-localized Energy of the Stringy Dyonic Black Hole Solution

In this article, we calculate the heat flux passing through the horizon $. {\bf TS}|_{r_h}$ and the difference of energy between the Einstein and Møller prescription within the region ${\cal M}$, in which is the region between outer horizon ${\cal H}_+$ and inner horizon ${\cal H}_-$, for the modified GHS solution, KLOPP solution and CLH solution. The formula . E_{\rm Einstein}|_{\cal M} = . E_{\rm Møller}|_{\cal M} - \sum_{\partial {\cal M}} {\bf TS}$ is obeyed for the mGHS solution and the KLOPP solution, but not for the CLH solution. Also, we suggest a RN-like stringy dyonic black hole solu…

A Study of Universal Thermodynamics in Massive Gravity: Modified Entropy on the Horizons

Universal thermodynamics for FRW model of the Universe bounded by apparent/event horizon has been considered for massive gravity theory. Assuming Hawking temperature and using the unified first law of thermodynamics on the horizon, modified entropy on the horizon has been determined. For simple perfect fluid with constant equation of state, generalized second law of thermodynamics and thermodynamical equilibrium have been examined on both the horizons.

Galactic Clustering Under Power-law Modified Newtonian Potential

We estimate galaxy clustering under a modified gravitational potential. In particular, the modifications in gravitational potential energy occur due to a power-law and cosmological constant terms. We derive a canonical partition function for the system of galaxies interacting under such a modified gravitational potential. Moreover, we compute various thermodynamical equation of states for the system. We do comparative analysis in order to emphasize the effect of corrections on thermodynamics of the system. Interestingly, the modifications in thermodynamical quantities are embedded in clusterin…

Consequences of Thermal Fluctuations of Well-Known Black Holes in Modified Gravity

Quantum fluctuation consequences have significant role in high-energy physics. These fluctuation often regarded as a correction of the infrared (IR) limit. Such correction contribute to the high-energy limit of thermodynamical quantities and the stability conditions of black holes. In this work, we analyze the thermal stability of black holes in the presence of thermal fluctuations. We consider AdS black hole in Born-Infeld massive gravity with non-abelian hair and the charged AdS black hole with a global monopole. We develop many thermodynamical quantities such as entropy, temperature, pressu…

Universal thermodynamics in different gravity theories: Conditions for generalized second law of thermodynamics and thermodynamical equilibrium on the horizons

The present work deals with a detailed study of universal thermodynamics in different modified gravity theories. The validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) of the Universe bounded by a horizon (apparent/event) in f(R)-gravity, Einstein-Gauss-Bonnet gravity, RS-II brane scenario and DGP brane model has been investigated. In the perspective of recent observational evidences, the matter in the Universe is chosen as interacting holographic dark energy model. The entropy on the horizons are evaluated from the validity of the unified firs…

Dynamical and Thermodynamical Aspects of Interacting Kerr Black Holes

We consider the asymptotically flat double-Kerr solution for two equal mass black holes with either the same or opposite angular momentum and with a massless strut between them. For fixed angular momentum and mass, the angular velocity of two co-rotating Kerr black holes decreases as they approach one another, from the Kerr value at infinite separation to the value of a single Kerr black hole with twice the mass and the angular momentum at the horizons merging limit. We show that the ratio J/M^2 for extremal co-rotating Kerr black holes varies from unity at infinite separation to two at the me…

$f\left( Q\right) $引力二次形式下Bianchi I型宇宙的热力学方面及观测约束

Thermodynamical aspects of Bianchi type-I Universe in quadratic form of $f\left( Q\right) $ gravity and observational constraints

本文在$f(Q)$引力框架下研究Bianchi I型宇宙学模型，采用$f(Q)=λQ^n$形式结合最新观测数据估算参数，并验证其热力学量与物理性质。

Thermodynamics of the inhomogeneous perfect fluid LTB model: Modified Bekenstein-Hawking system

The present work deals with three alternative generalized Bekenstein-Hawking formulation of thermodynamical parameters namely entropy and temperature for the universal thermodynamical system bounded by a horizon in the frame work of inhomogeneous perfect fluid Lemaitre-Tolman-Bondi (LTB) model of the Universe. For the first choice, the first law of thermodynamics holds only for the trivial de Sitter case of the LTB model while we need restriction on the evolution of the horizon radius for the validity of the generalized second law of thermodynamics. However, for the other two choices, the firs…

Particles in Loop Quantum Gravity formalism: a thermodynamical description

In this work, we analyse the thermodynamical behavior of massive and massless particles within Loop Quantum Gravity formalism. We investigate a modified dispersion relation which suffices to derive all our results of interest in an \textit{analytical} manner. Initially, we study the massive case where, in essence, we examine how the mass modifies the thermodynamical properties of the system. On the other hand, to the massless case, the thermodynamical system turns out to rely only on a specific thermal state quantity, the temperature. More so, the analysis of the spectral radiation, the equati…

Rindler修正的Schwarzschild黑洞热力学的领头阶修正

Leading-order corrections to the thermodynamics of Rindler modified Schwarzschild black hole

本研究针对Rindler修正的Schwarzschild黑洞，计算小热涨落下的热力学变量与领头阶修正，分析不同参数下的稳定性，证实热力学第一定律在热涨落中依然成立。

Modified (A)dS Schwarzschild black holes in Rainbow spacetime

A modified (Anti-)de Sitter Schwarzschild black hole solution is presented in the framework of rainbow gravity with a cosmological constant. Its thermodynamical properties are investigated. In general the temperature of modified black holes is dependent on the energy of probes which take the measurement. However, a notion of intrinsic temperature can be introduced by identifying these probes with radiation particles emitted from black holes. It is interesting to find that the Hawking temperature of this sort of black holes can be reproduced by employing the extended uncertainty principle and m…

Thermodynamical Aspects of Gravity: New insights

The fact that one can associate thermodynamic properties with horizons brings together principles of quantum theory, gravitation and thermodynamics and possibly offers a window to the nature of quantum geometry. This review discusses certain aspects of this topic concentrating on new insights gained from some recent work. After a brief introduction of the overall perspective, Sections 2 and 3 provide the pedagogical background on the geometrical features of bifurcation horizons, path integral derivation of horizon temperature, black hole evaporation, structure of Lanczos-Lovelock models, the c…

Thermodynamic Black Hole with Modified Chaplygin Gas as a Heat Engine

We assume that the negative cosmological constant as a thermodynamical pressure and the asymptotically anti-de Sitter (AdS) black hole thermodynamics with modified Chaplygin gas. We have written the mass of the black hole, volume, entropy and temperature due to the thermodynamic system. We find a new solution of Einstein's field equations of AdS black hole with modified Chaplygin gas as a thermodynamic system. We also examine the weak, strong and dominant energy conditions for the source fluid of black hole. We also show that the thermodynamic black hole with Chaplygin gas can be considered as…

Thermodynamical correspondence of $f(R)$ gravity in Jordan and Einstein frames

We study the thermodynamical aspects of $f(R)$ gravity in the Jordan and the Einstein frame, and we investigate the corresponding equivalence of the thermodynamical quantities in the two frames. We examine static spherically symmetric black hole solutions with constant Ricci scalar curvature $R$, and as we demonstrate, the thermodynamical quantities in the two frames are equivalent. However, for the case of black holes with non-constant scalar curvature $R$, the thermodynamical equivalence of the two frames is no longer valid. In addition, we examine cosmological solutions with non-trivial cur…

On the thermodynamics of scale factor dual Universes

The thermodynamical aspects of the conformal time scale factor duality (SFD) of cosmological models within Einstein Gravity are investigated. We derive the SFD transformations of the thermodynamical quantities describing the thermal evolution of the matter fluid and of the apparent horizon. The thermodynamical properties of the self-dual cosmological models with a modified Chaplygin gas are studied in detail. We deduce the restrictions on the equation of state parameters that allow to extend scale factor duality as a UV/IR symmetry of the cosmological models consistent with their thermodynamic…

Bardeen规则黑洞中的热力学测地线：常规与修正几何热力学度规的比较

Thermodynamic Geodesics in Bardeen Regular Black Hole: Conventional vs. Modified Geometrothermodynamics Metrics

本研究通过比较常规与修正的几何热力学度规，发现修正后的度规能更全面地反映Bardeen规则黑洞的热力学性质，包括温度消失线和旋节线等边界信息，是研究黑洞热力学行为的更优选择。

Black Hole Thermodynamics in MOdified Gravity (MOG)

We analyze the thermodynamical properties of black holes in a modified theory of gravity, which was initially proposed to obtain correct dynamics of galaxies and galaxy clusters without dark matter. The thermodynamics of non-rotating and rotating black hole solutions resembles similar solutions in Einstein-Maxwell theory with the electric charge being replaced by a new mass dependent gravitational charge $Q = \sqrt{αG_N}M$. This new mass dependent charge modifies the effective Newtonian constant from $G_N$ to $G = G_N(1+α)$, and this in turn critically affects the thermodynamics of the black h…

Modified gravity one-loop partition function

The one-loop partition function of the $f(R,R_{μν}R^{μν})$ gravity theory is obtained around AdS$_4$ background. After suitable choice of the gauge condition and computation of the ghost determinant, we obtain the one-loop partition function of the theory. The traced heat kernel over the thermal quotient of AdS$_4$ space is also computed and the thermal partition function is obtained for this theory. We have then consider quantum corrections to the thermodynamical quantities in some special cases.

Causality Aspects of Modified Kerr-Newman spacetimes

In this paper, we address the problem of causality violation in the solutions of Einstein equations and seek possible causality restoration mechanisms in modifed theories of gravity. We choose for the above problem, the causality violation due to the existence of closed time-like curves in the context of Kerr-Newman black hole. We first revisit and quantify the details of the causality violation in the Kerr-Newman spacetime. We then show that the issue is also existent in two of the modified solutions to the Kerr Newman spacetime: The Non-Commutativity inspired solution and the f(R)-Gravity mo…

Einstein-non-linear Maxwell-Yukawa black hole

Within the context of nonlinear electromagnetism we consider the Yukawa extension of a Reissner-Nordström black hole. Exact solution is given which modifies certain characteristics of the latter. Some thermodynamical aspects are given for comparison. The model may be considered as a useful agent to describe a short-ranged, charged, massive interaction.

Thermodynamical aspects of running vacuum models

The thermal history of a large class of running vacuum models in which the effective cosmological term is described by a truncated power series of the Hubble rate, whose dominant term is $Λ(H) \propto H^{n+2}$, is discussed in detail. Specifically, by assuming that the ultra-relativistic particles produced by the vacuum decay emerge into space-time in such a way that its energy density $ρ_r \propto T^{4}$, the temperature evolution law and the increasing entropy function are analytically calculated. For the whole class of vacuum models explored here we findthat the primeval value of the comovi…

Constant sound speed and its thermodynamical interpretation in $f(Q)$ gravity

On the basis of homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) geometry, solutions to the issues of cosmic acceleration and dark energy are being put forth within the context of $f\left( Q\right)$ gravity. We take into account a power law $f(Q)$ model using $f\left( Q\right) =αQ^{n}$, where $α$ and $n$ are free model parameters. In the current scenario, we may establish the energy density and pressure for our $f(Q)$ cosmic model by applying the constant sound speed parameterizations, i.e., $\vartheta_{s}^{2}=β$, where a barotropic cosmic fluid is described in terms of $β$…

Some Aspects of Virtual Black Holes

In this paper we shall consistently third quantize modified gravity. Then we shall analyse certain aspects of virtual black holes in this third quantized modified gravity. We will see how a statistical mechanical origin for the Bekenstein-Hawking entropy naturally arises in this model. Furthermore, in this model the area and thus the entropy of a real macroscopic black hole is quantized. Virtual black holes cause loss of quantum coherence and this gives an intrinsic entropy to all physical systems which can be used to define a direction of time and hence provide a solution to the problem of ti…

A modified thermodynamics of rotating and charged BTZ black hole

We present the thermodynamics of a charged and rotating BTZ black holes here. In particular, we derive expressions for various macroscopic thermal quantities such as entropy, Hawking temperature, Helmholtz free energy, internal energy, enthalpy, Gibbs free energy, and specific heat. To study the effects of small statistical thermal fluctuations around the equilibrium on thermodynamics, we calculated the leading-order corrections to the various thermodynamical potentials of charged and rotating BTZ black hole and do comparative analysis for the fixed values of charge and angular momentum.

Reissner Nordstrom Metric in Unimodular Theory of Gravity

We study the modified Reissner Nordstrom metric in the unimodular gravity. So far the spherical symmetric Einstein field equation in unimodular gravity has been studied in the absence of any source. We consider static electric and magnetic charge as source. We solve for Maxwell equations in unimodular gravitational background. We show that in unimodular gravity the electromagnetic field strength tensor is modified. We also show that the solution in unimodular gravity differs from the usual R-N metric in Einstein gravity with some corrections. We further study the thermodynamical properties of …

Two-Fluid Viscous Modified Gravity on a RS Brane

Singularities in the dark energy late universe are discussed, under the assumption that the Lagrangian contains the Einstein term R plus a modified gravity term R^α, where αis a constant. The 4D fluid is taken to be viscous and composed of two components, one Einstein component where the bulk viscosity is proportional to the scalar expansion θ, and another modified component where the bulk viscosity is proportional to the power θ^{2α-1}. Under these conditions it is known from earlier that the bulk viscosity can drive the fluid from the quintessence region (w > -1) into the phantom region (w<-…

非对易规范理论中修正的黑洞热力学第一定律

On Modified First Law of Black hole Thermodynamics in The Non-Commutative Gauge Theory

本文在非对易引力规范理论中引入与 Θ 共轭的 NC 势修正黑洞热力学第一定律，揭示 NC Schwarzschild 黑洞的相变、蒸发末期行为及 Θ 的热力学变量作用。

Aspects of String-Gas Cosmology at Finite Temperature

We study string-gas cosmology in dilaton gravity, inspired by the fact that it naturally arises in a string theory context. Our main interest is the thermodynamical treatment of the string-gas and the resulting implications for the cosmology. Within an adiabatic approximation, thermodynamical equilibrium and a small, toroidal universe as initial conditions, we numerically solve the corresponding equations of motions in two different regimes describing the string-gas thermodynamics: (i) the Hagedorn regime, with a single scale factor, and (ii) an almost-radiation dominated regime, which include…

Higher dimensional dyonic black holes

The paper at hand presents a novel class of dyonic black holes in higher dimensions through a new proposal for the electromagnetic field tensor. The black hole solutions are extracted analytically and their geometrical/physical properties are studied. In addition, the details regarding thermodynamical structure and phase transition behavior of the solutions for $4$ different cases are investigated: i) general case, ii) constant electric field, iii) constant magnetic field, and iv) constant electric and magnetic fields. It will be shown that depending on the picture under consideration, the the…

Some Thermodynamic Aspects of Black Holes and Singularities

We review and correct the classical critical exponents characterizing the transition from negative to positive black hole's heat capacity at high charge--angular momentum. We discuss the stability properties of black holes as a thermodynamic system in equilibrium with a radiation bath (canonical ensamble) by using the Helmholtz free energy potential. We finally analytically extend the analysis to negative mass holes and study its thermodynamical stability behavior.

Affine quantization of Black Holes: thermodynamics, singularity removal and displaced horizons

In this work we investigate the thermodynamical properties and modified dynamics of black hole solutions in the semiclassical regime of affine coherent state quantization. Using the weak correspondence principle we build a semiclassical effective action that we use to study thermodynamics in the canonical ensemble and to compare classical analytical solutions with the corresponding semiclassical ones. We determine a strong compatibility of these affine black holes with the thermodynamical properties of the classical counterparts, with only minor restrictions on the free parameters of the model…

毛状黑洞的热稳定性

On Thermal Stability of Hairy Black Holes

本文研究毛状黑洞的热力学稳定性，考虑次级毛的反作用，推导其与热浴达到稳定平衡的条件，并探讨其对量子时空最小长度的启示。

Modified Newtonian Dynamics as an entropic force

Under natural assumptions on the thermodynamic properties of space and time with the holographic principle we reproduce a MOND-like behaviour of gravity on particular scales of mass and length, where Newtonian gravity requires a modification or extension if no dark matter component is introduced in the description of gravitational phenomena. The result is directly obtained with the assumption that a fundamental constant of nature with dimensions of acceleration needs to be introduced into gravitational interactions. This in turn allows for modifications or extensions of the equipartion law and…

Some aspects of modified theory of gravity in Palatini formalism unveiled

Under conformal transformation, f(R) theory of gravity in Palatini formalism leads to a Brans-Dicke type of scalar-tensor equivalent theory with a wrong sign in the effective kinetic energy term. This means, the effective scalar acts as the dark energy and so late-time cosmic acceleration in matter-dominated era is accountable. However, we unveil some aspects of Palatini formalism, which clearly reveals the fact that the formalism is not suitable to explain the cosmological evolution of the early universe with $f(\mathfrak{R})$ gravity alone. Additionally, it is noticed that some authors, in a…

Study of General Relativity and $f(R)$ Modified Gravity with Cosmological Constant for Einstein and Jordan Frames

This thesis investigates a toy model for inflation in a class of modified theories of gravity in the metric formalism. Instead of the standard procedure -- assuming a non-linear Lagrangian $f(R)$ in the Jordan frame -- we start from a simple ϕ^2 potential in the Einstein frame and investigate the corresponding $f(R)$ in the former picture. Such approach yields plenty of new pieces of information, namely a self-terminating inflationary solution with a linear Lagrangian, a robust criterion for stability of such theories, a dynamical effective potential for the Ricci scalar $R$, the addition of a…

Regular Multi-Horizon Black Holes in Modified Gravity with Non-Linear Electrodynamics

We investigated the regular multi-horizon black holes in the Einstein gravity, $F(R)$ gravity and the 5 dimensional Gauss-Bonnet gravity, all of them coupled with non-linear electrodynamics. We presented several explicit examples of the actions which admit the solutions describing regular black hole space-time with multi-horizons. Thermodynamics of the obtained black hole solutions is studied. The explicit expressions of the temperature, the entropy, the thermodynamical energy and the free energy are obtained. Although the temperature vanishes in the extremal limit where the radii of the two h…

Thermodynamical Laws in Horava-Lifshitz Gravity

In this work, we have investigated the validity of GSL of thermodynamics in a universe (open, closed and flat) governed by Ho$\check{\text r}$ava-Lifshitz gravity. If the universe contains barotropic fluid the corresponding solutions have been obtained. The validity of GSL have been examined by two approaches: (i) robust approach and (ii) effective approach. In robust approach, we have considered the universe contains only matter fluid and the effect of the gravitational sector of HL gravity was incorporated through the modified black hole entropy on the horizon. Effective approach is that all…

Barrow's black hole entropy and the equipartition theorem

The Barrow entropy appears from the fact that the black hole surface can be modified due to quantum gravitational outcome. The measure of this perturbation is given by a new exponent $Δ$. In this letter we have shown that, from the standard mathematical form of the equipartition theorem, we can relate it with Barrow entropy. From this equivalence, we have calculated precisely the value of the exponent for the equipartition law. After that, we tested the thermodynamical coherence of the system by calculating the heat capacity which established an interval of the possible thermodynamical coheren…

远平行引力及其扩展的宇宙学与动力学方面

Cosmological and Dynamical Aspects of Teleparallel Gravity and its Extension

本论文研究含标量场与能量-动量张量迹的修正远平行引力模型，通过动力学系统分析其宇宙晚期加速效应，验证模型可行性并拓展宇宙动力学研究。

Some aspects of pre big bang cosmology

This is a summary of a course given at the Fourth Mexican School on Gravitation and Mathematical Physics on some aspects of PBB cosmology. After introductory remarks the lectures concentrate on some amusing consequences derived from the symmetries of the string theory with respect to such classical concepts as isotropy and homogeneity. The extra dimensions and the symmetries of the M theory are further applied to show that the classical singularities might be just physically irrelevant. In the final lecture a model universe is "produced" from "almost nothing" and it is argued that initial plan…

A Subtle Aspect of Minimal Lengths in the Generalized Uncertainty Principle

In this work, we point out an overlooked and subtle feature of the generalized uncertainty principle (GUP) approach to quantizing gravity: namely that different pairs of modified operators with the same modified commutator, $[\hat{X},\hat{P}] = i \hbar (1+βp^2)$, may have different physical consequences such as having no minimal length at all. These differences depend on how the position and/or momentum operators are modified rather than only on the resulting modified commutator. This provides guidance when constructing GUP models since it distinguishes those GUPs that have a minimal length sc…

On Aspects of Infinite Derivatives Field Theories & Infinite Derivative Gravity

Infinite derivative theory of gravity is a modification to the general theory of relativity. Such modification maintains the massless graviton as the only true physical degree of freedom and avoids ghosts. Moreover, this class of modified gravity can address classical singularities. In this thesis some essential aspects of an infinite derivative theory of gravity are studied. Namely, we considered the Hamiltonian formalism, where the true physical degrees of freedom for infinite derivative scalar models and infinite derivative gravity are obtained. Furthermore, the Gibbons-Hawking-York boundar…

Aspects of non-singular bounce in modified gravity theories

Scenario of a bouncing universe is one of the most active area of research to arrive at singularity free cosmological models. Different proposals have been suggested to avoid the so called 'big bang' singularity through the quantum aspect of gravity which is yet to have a proper understanding. In this work, on the contrary, we consider three different approaches, each of which goes beyond General Relativity but remain within the domain of classical cosmological scenario, to address this problem. The hallmark of all these approaches is that the origin of the bouncing mechanism is somewhat natur…

Modified gravity or modified matter ?

To the astrophysicist faced with the puzzle of dark matter, this one appears under two different aspects: on the one hand in cosmology, i.e. at very large scales, where it seems to be made of a bath of particles; on the other hand at the scale of galaxies, where it is described by a set of specific phenomena, looking incompatible with a description in terms of particles, and suggesting that we are seeing a modification of the law of gravity. Reconciling these two distinct aspects of dark matter in a single theoretical formalism is an important challenge which could lead to some new physics in …

Modified gravity and binary pulsars: the Lorentz violating case

The dynamics of binary pulsars can be used to test different aspects of gravitation. This is particularly important to constrain alternatives to general relativity in regimes which are not probed by other methods. In this short contribution, I will describe the case of theories of gravity without Lorentz invariance. The latter are important in the context of quantum gravity and modify the laws of gravity at basically all scales.

Thermodynamics of Schwarzschild-like black holes in modified gravity models

Over the last decades, many methods were developed to prove Hawking radiation. Recently, a semiclassical method known as the tunneling method has been proposed as a more straightforward way of derivating black hole thermodynamical properties. This method has been widely applied to a vast sort of spacetimes with satisfactory results. In this work, we obtain the black hole thermodynamics in the presence of a Lorentz symmetry breaking (LSB). We apply the Hamilton-Jacobi method to Schwarzschild-like black holes, and we investigate whether the LSB affects their thermodynamics. The results found sho…