Dynamic study of Weyl tensor corrected f(R) gravity

We investigate the cosmological and thermodynamic aspects of Weyl tensor corrected [Formula: see text] gravity. For this purpose, we assume some well-known cosmological bouncing scenarios such as symmetric bounce cosmology, oscillatory cosmology, matter bounce cosmology, little rip cosmology, superbounce cosmology and develop some cosmological parameters. For instance, the equation of state parameter [Formula: see text] describes the quintessence phase for symmetric bounce cosmology, vacuum phase for oscillatory, little rip and matter bounce cosmology while it gives both quintessence and vacuum phases for matter bounce cosmology. It is also observed that the squared speed of sound [Formula: see text] gives positive behavior for all models resulting in that the models assumed are stable. We evaluate generalized second law of thermodynamics which remains valid for all cosmological models except symmetric bounce cosmology. Moreover, we also investigate the thermal equilibrium condition [Formula: see text] and found its validity for all models except symmetric bounce cosmological model.

Qualitative aspects of Rastall gravity with barotropic fluid

We investigate the dynamical evolution of homogeneous and isotropic flat-FRW universe filled with a barotropic fluid satisfying linear equation of state in Rastall gravity. Using dynamical system approach, we find the fixed points of the system and study their stability. We further explore the thermodynamic aspects at the apparent horizon by investigating the validity of generalized second law of thermodynamics with equilibrium description.

Particle creation from thermodynamics point of view in f(𝒢,T) gravity

This paper aims to discuss the gravitationally induced particle creation in the framework of [Formula: see text] theory, which involves the non-minimal coupling (NMC) between Gauss–Bonnet (GB) invariant, [Formula: see text] and trace of the energy–momentum tensor (EMT), [Formula: see text]. Here, NMC between matter and gravitational sector results in non-divergence of EMT. We discuss the generalized conservation equation for the irreversible process of matter creation with the help of generalized second law of thermodynamics (GSLT). Particle creation rate, creation pressure, entropy production rate and temperature are obtained for this theory using flat FRW geometry. We work on three particular [Formula: see text] models and study cosmological implications of open irreversible thermodynamics. Furthermore, the impact of NMC on cosmological evolution and entropy production is briefly discussed.

The generalized second law of thermodynamics with Barrow entropy

We investigate the validity of the generalized second law of thermodynamics, applying Barrow entropy for the horizon entropy. The former arises from the fact that the black-hole surface may be deformed due to quantum-gravitational effects, quantified by a new exponent $$\Delta $$ Δ . We calculate the entropy time-variation in a universe filled with the matter and dark energy fluids, as well as the corresponding quantity for the apparent horizon. We show that although in the case $$\Delta =0$$ Δ = 0 , which corresponds to usual entropy, the sum of the entropy enclosed by the apparent horizon plus the entropy of the horizon itself is always a non-decreasing function of time and thus the generalized second law of thermodynamics is valid, in the case of Barrow entropy this is not true anymore, and the generalized second law of thermodynamics may be violated, depending on the universe evolution. Hence, in order not to have violation, the deformation from standard Bekenstein–Hawking expression should be small as expected.

The barrow holographic dark energy-based reconstruction of f(R) gravity and cosmology with Nojiri–Odintsov cutoff

In the work reported here we have considered Barrow holographic dark energy (BHDE) proposed in E. N. Saridakis, Barrow holographic dark energy, Phys. Rev. D 102 (2020) 123525 as a special case of more generalized version of Nojiri–Odintsov holographic dark energy (NOHDE) proposed in S. I. Nojiri and S. D. Odintsov, Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285–1304 and also reconstructed [Formula: see text] gravity with BHDE as the form of background evolution. It has been observed that in the case of BHDE reconstructed [Formula: see text] gravity the equation of state can have a transition from quintessence to phantom. In a particular case of reconstruction, possibility of Little Rip singularity has been observed. Finally, the generalized second law of thermodynamics has been found to be valid under this reconstruction scheme.

Cosmological consequences of modified Friedmann equations according to holographic equipartition law

We examine thermodynamically an extra driving term for the flat universe by applying Sharma Mittal entropy to Padmanabhan’s holographic equipartition law. Deviations from the Bekenstein–Hawking entropy by using this law, we generate an extra driving in the acceleration equation. By using the constant and parametrized equation of state parameter, we investigate the different cosmological parameters like deceleration parameter, squared speed of sound, Om-diagnostic and statefinder parameter through graphical approach. We observe compatible results with current observational data in both models. Generalized second law of thermodynamics also remains valid in both cases.

Hawking radiation from universal horizons

The persistence of a suitable notion of black hole thermodynamics in Lorentz breaking theories of gravity is not only a non-trivial consistency test for such theories, it is also an interesting investigation per se, as it might help us identifying the crucial features at the root of these surprising laws governing such purely gravitational objects. In past investigations, controversial findings were presented in this sense. With the aim of settling this issue, we present here two complementary derivations of Hawking radiation in geometries endowed with universal horizons: a novel feature of back holes in Lorentz breaking theories of gravity which reproduces several properties normally characterizing Killing horizons. We find that both the derivations agree on the fact that the Hawking temperature associated to these geometries is set by the generalized universal horizon peeling surface gravity, as required for consistency with extant derivations of the first law of thermodynamics for these black holes. We shall also comment on the compatibility of our results with previous alternative derivations and on their significance for the survival of the generalized second law of black hole thermodynamics in Lorentz breaking theories of gravity.

The Entropy of Supermassive Black Holes during its Evaporation Time

Is it possible to quantify in General Relativity, GR, the entropy generated by supermassive black holes, BHs, during its evaporation time, since the intrinsic Hawking radiation in the infinity that, although insignificant, is important in the effects on the thermal quantum atmosphere?The purpose was to develop a formula that allows us to measure the entropy generated during the evaporation time of different types of BHs of: i. remnant BH of the binary black holes’ merger, BBH: GW150914, GW151226 and LTV151012 detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), and ii. Schwarzschild, Reissner-Nordström, Kerr and Kerr-Newman, and thus quantify in GR the “insignificant” quantum effects involved, in order to contribute to the validity of the generalized second law (GSL) that directly links the laws of black hole mechanics to the ordinary laws of thermodynamics, as a starting point for unifying quantum effects with GR. This formula could have some relationship with the detection of the shadow’s image of the event horizon of a BH.This formula was developed in dimensional analysis, using the constants of nature and the possible evaporation time of a black hole, to quantify the entropy generated during that time. The energy-stress tensor was calculated with the 4 metrics to obtain the material content and apply the proposed formula.The entropy of the evaporation time of BHs proved to be insignificant, its temperature is barely above absolute zero, however, the calculation of this type of entropy allows us to argue about the importance of the quantum effects of Hawking radiation mentioned by authors who have studied the quantum effects with arguments that are fundamentally based on the presence of the surrounding thermal atmosphere of the black hole.