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J. P. Morais Graça

Publications and source records attributed to J. P. Morais Graça.

At least 19 recordsLinked to original sources
arXiv2024

Joule-Thomson expansion for quantum corrected AdS-Reissner-Nordstrom black holes in Kiselev spacetime

In this work we study the inversion temperature associated with the Joule-Thomson expansion from the thermodynamics of AdS-Reissner-Nördstrom black holes. We include quantum corrections in a cosmological fluid that can describe phantom dark matter or quintessence, both in a Kiselev scenario. The description of such physical systems involves numerical solutions and the results are presented as temperature-pressure plots for various values of the parameters of our model. We find non-zero minimum inversion temperatures as well as non-zero minimum pressures depending on the values of those parameters. Completing our study, we also find isenthalpic curves associated with black hole fixed mass processes.

gr-qc↗
arXiv2022

The third law of thermodynamics, non-extensivity, and energy definition in black hole physics

Working in the framework of generalized statistics, the problem of establishing the third law of thermodynamics in the black hole physics is studied by focusing on Schwarzschild black hole which easily and clearly exposes the violation of this law in the common approach based on Bekenstein entropy. Additionally, it is addressed that some inconsistencies between the predictions of quantum field theory and thermodynamics about the black hole temperature may be reconciled by using the thermodynamics laws in order to broaden energy definition. It claims that thermodynamics should be employed as a powerful tool in looking for more comprehensive energy definitions in high-energy physics, still mysterious.

gr-qc↗
arXiv2022

AdS/QCD oddball masses and Odderon Regge trajectory from a twist-five operator approach

In this work, we consider a massive gauge boson field in AdS$_5$ dual to odd glueball states with twist-5 operator in 4D Minkowski spacetime. Introducing an IR cutoff we break the conformal symmetry of the boundary theory allowing us to calculate the glueball masses with odd spins using Dirichlet and Neumann boundary conditions. Then, from these masses we construct the corresponding Regge trajectories associated with the odderon. Our results are compatible with the ones in the literature.

hep-th↗
arXiv2021

Joule-Thomson expansion for noncommutative uncharged black holes

In this work we study the Joule-Thomson expansion for uncharged black holes in a noncommutative scenario characterized by a parameter $θ$, which is present in the horizon function. We calculate the inversion temperature for some values of $θ$ and the isenthalpics for fixed masses. We find that the uncharged noncommutative black hole behaves as a charged commutative one.

hep-th↗
arXiv2021

The extended phase space thermodynamics of Planck-scale-corrected Reissner-Nordström-anti-de Sitter black hole

We analyze the effect of Planck-scale modified radiation equation of state on the Reissner-Nodström-anti-de Sitter black hole inspired by Kiselev's ansatz. Deformed thermodynamic quantities are found, phase transitions and black holes as heat engines are described for the Carnot and square cycles. Non-trivial differences between linear and quadratic Planck-scale corrections are discussed in detail.

gr-qc↗
arXiv2021

Thermodynamics and remnants of Kiselev black holes in Rainbow gravity

We do a detailed study of the thermodynamics of black holes in Rainbow gravity in the framework of the Kiselev metric, taking into account different cosmic fluids which can mimic several kinds of dark energy scenarios. A discussion related to the appearance of black hole remnants is presented and, unlike other studies on the same topic, we found no evidence of the appearance of remnants in Rainbow gravity, except in peculiar cases.

gr-qc↗
arXiv2020

Thin-shell wormholes in Rastall gravity

We constructed thin-shell wormholes using the well-known "cut and paste" technique for static black holes sourced by an anisotropic fluid within the context of the Rastall gravity. Using the generalized Lanczos equations we explored the energy conditions at the wormhole's throat along with the traversability condition. We determined the stability regions when the wormhole configurations are surrounded by different bulk sources and obtained that the stability regions are considerably modified due to the non-trivial dependence of the Rastall parameter in the effective potential energy.

gr-qc↗
arXiv2020

Effects of Planck-scale-modified dispersion relations on the thermodynamics of charged black holes

Considering corrections produced by modified dispersion relations on the equation of state parameter of radiation, we study the induced black hole metric inspired by Kiselev's ansatz, thus defining a deformed Reissner-Nordström metric. In particular, we consider thermodynamic properties of such a black hole from the combined viewpoints of the modified equation of state parameter and the phenomenological approach to the quantum gravity problem called rainbow gravity.

gr-qc↗
arXiv2019

Effects of quantum corrections on the criticality and efficiency of black holes surrounded by a perfect fluid

We study some properties of the extended phase space of a quantum-corrected Schwarzschild black hole surrounded by a perfect fluid. In particular we demonstrate that, due to the quantum correction, there exist first and second order phase transitions for a certain range of the state parameter of the perfect fluid, and we explicitly analyze some cases. Besides that, we describe the efficiency of this system as a heat engine and the effect of quantum corrections for different surrounding fluids.

gr-qc↗
arXiv2018

Tsallis holographic dark energy in the brane cosmology

We study some cosmological features of Tsallis holographic dark energy (THDE) in Cyclic, DGP and RS II braneworlds. In our setup, a flat FRW universe is considered filled by a pressureless source and THDE with the Hubble radius as the IR cutoff, while there is no interaction between them. Our result shows that although suitable behavior can be obtained for the system parameters such as the deceleration parameter, the models are not always stable during the cosmic evolution at the classical level.

physics.gen-ph↗
arXiv2018

Thermodynamic approach to holographic dark energy and the Rényi entropy

Using the first law of thermodynamics, we propose a relation between the system entropy ($S$) and its IR ($L$) and UV ($Λ$) cutoffs. In addition, applying this relation to the apparent horizon of flat FRW universe, whose entropy meets the Rényi entropy, a new holographic dark energy model is addressed. Thereinafter, the evolution of the flat FRW universe, filled by a pressureless source and the obtained dark energy candidate, is studied. In our model, there is no mutual interaction between the cosmos sectors. We find out that the obtained model is theoretically powerful to explain the current accelerated phase of the universe. This result emphasizes that the generalized entropy formalism is suitable for describing systems including the long-range interactions such as gravity.

physics.gen-ph↗
arXiv2018

Tsallis holographic dark energy in the Brans-Dicke cosmology

Using the Tsallis generalized entropy, holographic hypothesis and also considering the Hubble horizon as the IR cutoff, we build a holographic model for dark energy and study its cosmological consequences in the Brans-Dicke framework. At first, we focus on a non-interacting universe, and thereinafter, we study the results of considering a sign-changeable interaction between the dark sectors of the cosmos. Our investigations show that, compared with the flat case, the power and freedom of the model in describing the cosmic evolution is significantly increased in the presence of the curvature. The stability analysis also indicates that, independent of the universe curvature, both the interacting and non-interacting cases are classically unstable. In fact, both the classical stability criterion and an acceptable behavior for the cosmos quantities, including the deceleration and density parameters as well as the equation of state, are not simultaneously obtainable.

gr-qc↗
arXiv2018

Energy definition and dark energy: a thermodynamic analysis

Accepting the Komar mass definition of a source with energy-momentum tensor $T_{μν}$, and using the thermodynamic pressure definition, we find a relaxed energy-momentum conservation law. Thereinafter, we study some cosmological consequences of the obtained energy-momentum conservation law. It has been found out that the dark sectors of cosmos are unifiable into one cosmic fluid in our setup. While this cosmic fluid impels the universe to enter an accelerated expansion phase, it may even show a baryonic behavior by itself during the cosmos evolution. Indeed, in this manner, while $T_{μν}$ behaves baryonically, some parts of it, namely $T_{μν}(e)$ which is satisfying the ordinary energy-momentum conservation law, are responsible for the current accelerated expansion.

physics.gen-ph↗
arXiv2018

Cloud of strings in f(R) gravity

We derive the solution for a spherically symmetric string cloud configuration in a d-dimensional spacetime in the framework of f(R) theories of gravity. We also analyze some thermodynamic properties of the joint black hole - cloud of strings solution. For its Hawking temperature, we found that the dependence of the mass with the horizon is significantly different in both theories. For the interaction of a black hole with thermal radiation, we found that the shapes of the curves are similar, but shifted. Our analysis generalizes some known results in the literature.

gr-qc↗
arXiv2018

Thermodynamics of Black Holes in Rastall Gravity

A promising theory in modifying general relativity by violating the ordinary energy-momentum conservation law in curved spacetime is the Rastall theory of gravity. In this theory, geometry and matter fields are coupled to each other in a non-minimal way. Here, we study thermodynamic properties of some black hole solutions in this framework, and compare our results with those of general relativity. We demonstrate how the presence of these matter sources may amplify effects caused by the Rastall parameter in thermodynamic quantities. Our investigation also shows that black holes with radius smaller than a certain amount ($\equiv r_0$) have negative heat capacity in the Rastall framework. In fact, it is a lower bound for the possible values of horizon radius satisfied by stable black holes.

gr-qc↗
arXiv2018

Generalized entropy formalism and a new holographic dark energy model

Recently, the Rényi and Tsallis generalized entropies have extensively been used in order to study various cosmological and gravitational setups. Here, using a special type of generalized entropy, a generalization of both the Rényi and Tsallis entropy, together with holographic principle, we build a new model for holographic dark energy. Thereinafter, considering a flat FRW universe, filled by a pressureless component and the new obtained dark energy model, the evolution of cosmos has been investigated showing satisfactory results and behavior. In our model, the Hubble horizon plays the role of IR cutoff, and there is no mutual interaction between the cosmos components. Our results indicate that the generalized entropy formalism may open a new window to become more familiar with the nature of spacetime and its properties.

gr-qc↗
arXiv2017

Scalar QNMs for higher dimensional black holes surrounded by quintessence in Rastall gravity

The spacetime solution for a black hole, surrounded by an exotic matter field, in Rastall gravity, is calculated in an arbitrary d-dimensional spacetime. After this, we calculate the scalar quasinormal modes of such solution, and study the shift on the modes caused by the modification of the theory of gravity, i.e., by the introduction of a new term due to Rastall. We conclude that the shift strongly depends on the kind of exotic field one is studying, but for a low density matter that supposedly pervades the universe, it is unlikely that Rastall gravity will cause any instability on the probe field.

gr-qc↗