arXiv subjects

S. H. Hendi

Publications and source records attributed to S. H. Hendi.

At least 73 records · Page 4Linked to original sources

arXiv2016

Phase transition of charged Black Holes in Brans-Dicke theory through geometrical thermodynamics

In this paper, we take into account black hole solutions of Brans-Dicke-Maxwell theory and investigate their stability and phase transition points. We apply the concept of geometry in thermodynamics to obtain phase transition points and compare its results with those, calculated in canonical ensemble through heat capacity. We show that these black holes enjoy second order phase transitions. We also show that there is a lower bound for the horizon radius of physical charged black holes in Brans-Dicke theory which is originated from restrictions of positivity of temperature. In addition, we find that employing specific thermodynamical metric in the context of geometrical thermodynamics, yields divergencies for thermodynamical Ricci scalar in places of the phase transitions. It will be pointed out that due to characteristics behavior of thermodynamical Ricci scalar around its divergence points, one is able to distinguish the physical limitation point from the phase transitions. In addition, the free energy of these black holes will be obtained and its behavior will be investigated. It will be shown that the behavior of the free energy in the place where the heat capacity diverges, demonstrates second order phase transition characteristics.

gr-qc↗

arXiv2016

Extended phase space thermodynamics and $P-V$ criticality: Brans-Dicke-Born-Infeld vs Einstein-Born-Infeld-dilaton black holes

Motivated by thermodynamic analogy of black holes and Van der Waals liquid/gas system, in this paper, we study $P-V$ criticality of both dilatonic Born-Infeld black holes and their conformal solutions, Brans-Dicke-Born-Infeld solutions. Due to the conformal constraint, we have to neglect the old Lagrangian of dilatonic Born-Infeld theory and its black hole solutions, and introduce a new one. We obtain spherically symmetric nonlinearly charged black hole solutions in both Einstein and Jordan frames and then, we calculate the related conserved and thermodynamic quantities. After that, we extend the phase space by considering the proportionality of the cosmological constant and thermodynamical pressure. We obtain critical values of thermodynamic coordinates through numerical methods and plot relevant $P-V$ and $G-T$ diagrams. Investigation of the mentioned diagrams helps us to study thermodynamical phase transition. We also analyze the effects of varying different parameters on the phase transition of black holes.

gr-qc↗

arXiv2016

Charged Dilatonic Black Holes in Gravity's Rainbow

In this paper, we present charged dilatonic black holes in gravity's rainbow. We study geometric and thermodynamic properties of black hole solutions. We also investigate the effects of rainbow functions on different thermodynamic quantities for these charged black holes in dilatonic gravity's rainbow. Then, we demonstrate that first law of thermodynamics is valid for these solutions. After that, we investigate thermal stability of the solutions using canonical ensemble and analyze the effects of different rainbow functions on thermal stability. In addition, we present some arguments regarding the bound and phase transition points in context of geometrical thermodynamics. We also study the phase transition in extended phase space in which cosmological constant is treated as the thermodynamic pressure. Finally, we use another approach to calculate and demonstrate that obtained critical points in extended phase space are representing a second order phase transition for these black holes.

hep-th↗

arXiv2016

Massive charged BTZ black holes in asymptotically (a)dS spacetimes

Motivated by recent developments of BTZ black holes and interesting results of massive gravity, we investigate massive BTZ black holes in the presence of Maxwell and Born-Infeld (BI) electrodynamics. We study geometrical properties such as type of singularity and asymptotical behavior as well as thermodynamic structure of the solutions through canonical ensemble. We show that despite the existence of massive term, obtained solutions are asymptotically (a)dS and have a curvature singularity at the origin. Then, we regard varying cosmological constant and examine the Van der Waals like behavior of the solutions in extended phase space. In addition, we employ geometrical thermodynamic approaches and show that using Weinhold, Ruppeiner and Quevedo metrics leads to existence of ensemble dependency while HPEM metric yields consistent picture. For neutral solutions, it will be shown that generalization to massive gravity leads to the presence of non-zero temperature and heat capacity for vanishing horizon radius. Such behavior is not observed for linearly charged solutions while generalization to nonlinearly one recovers this property.

hep-th↗

arXiv2016

Extended phase space of AdS Black Holes in Einstein-Gauss-Bonnet gravity with a quadratic nonlinear electrodynamics

In this paper, we consider quadratic Maxwell invariant as a correction to the Maxwell theory and study thermodynamic behavior of the black holes in Einstein and Gauss-Bonnet gravities. We consider cosmological constant as a thermodynamic pressure to extend phase space. Next, we obtain critical values in case of variation of nonlinearity and Gauss-Bonnet parameters. Although the general thermodynamical behavior of the black hole solutions is the same as usual Van der Waals system, we show that in special case of the nonlinear electromagnetic field, there will be a turning point for the phase diagrams and usual Van der Waals is not observed. This theory of nonlinear electromagnetic field provides two critical horizon radii. We show that this unusual behavior of phase diagrams is due to existence of second critical horizon radius. It will be pointed out that the power of the gravity and nonlinearity of the matter field modify the critical values. We generalize the study by considering the effects of dimensionality on critical values and make comparisons between our models with their special sub classes. In addition, we examine the possibility of the existence of the reentrant phase transitions through two different methods.

gr-qc↗

arXiv2016

Thermodynamic instability of nonlinearly charged black holes in gravity's rainbow

Motivated by the violation of Lorentz invariancy in quantum gravity, we study black hole solutions in gravity's rainbow in context of Einstein gravity coupled with various models of nonlinear electrodynamics. We regard an energy dependent spacetime and obtain related metric functions and electric fields. We show that there is an essential singularity at the origin which is covered with an event horizon. We also compute the conserved and thermodynamical quantities and examine the validity of the first law of thermodynamics in the presence of rainbow functions. Finally, we investigate thermal stability conditions for these black hole solutions in context of canonical ensemble. We show that thermodynamical structure of the solutions depends on the choices of nonlinearity parameters, charge and energy functions.

gr-qc↗

arXiv2016

Charged Black Hole Solutions in Gauss-Bonnet-Massive Gravity

Motivated by high interest in the close relation between string theory and black hole solutions, in this paper, we take into account the Einstein-Gauss-Bonnet Lagrangian in the context of massive gravity. We examine the possibility of black hole in this regard, and discuss the types of horizons. Next, we calculate conserved and thermodynamic quantities and check the validity of the first law of thermodynamics. In addition, we investigate the stability of these black holes in context of canonical ensemble. We show that number, type and place of phase transition points may be significantly affected by different parameters. Next, by considering cosmological constant as thermodynamical pressure, we will extend phase space and calculate critical values. Then, we construct thermodynamical spacetime by considering mass as thermodynamical potential. We study geometrical thermodynamics of these black holes in context of heat capacity and extended phase space. We show that studying heat capacity, geometrical thermodynamics and critical behavior in extended phase space lead to consistent results. Finally, we will employ a new method for obtaining critical values and show that the results of this method are consistent with those of other methods.

hep-th↗

arXiv2015

Extended phase space of Black Holes in Lovelock gravity with nonlinear electrodynamics

In this paper, we consider Lovelock gravity in presence of two Born-Infeld types of nonlinear electrodynamics and study their thermodynamical behavior. We extend the phase space by considering cosmological constant as a thermodynamical pressure. We obtain critical values of pressure, volume and temperature and investigate the effects of both the Lovelock gravity and the nonlinear electrodynamics on these values. We plot $P-v$, $T-v$ and $G-T$ diagrams to study the phase transition of these thermodynamical systems. We show that power of the nonlinearity and gravity have opposite effects. We also show how considering cosmological constant, nonlinearity and Lovelock parameters as thermodynamical variables will modify Smarr formula and first law of thermodynamics. In addition, we study the behavior of universal ratio of $\frac{P_{c}v_{c}}{T_{c}}$ for different values of nonlinearity power of electrodynamics as well as the Lovelock coefficients.

gr-qc↗

arXiv2015

A new approach toward geometrical concept of black hole thermodynamics

Motivated by the energy representation of Riemannian metric, in this paper we study different approaches toward the geometrical concept of black hole thermodynamics. We investigate thermodynamical Ricci scalar of Weinhold, Ruppeiner and Quevedo metrics and show that their number and location of divergences do not coincide with phase transition points arisen from heat capacity. Next, we introduce a new metric to solve these problems. We show that the denominator of the Ricci scalar of the new metric contains terms which coincide with different types of phase transitions. We elaborate the effectiveness of the new metric and shortcomings of the previous metrics with some examples. Furthermore, we find a characteristic behavior of the new thermodynamical Ricci scalar which enables one to distinguish two types of phase transitions. In addition, we generalize the new metric for the cases of more than two extensive parameters and show that in these cases the divergencies of thermodynamical Ricci scalar coincide with phase transition points of the heat capacity.

gr-qc↗

arXiv2015

Phase transition and thermodynamic geometry of Einstein-Maxwell-dilaton black holes

In this paper, we consider a linearly charged dilatonic black holes and study their thermodynamical behavior in the context of phase transition and thermodynamic geometry. We show that, depending on the values of the parameters, these type of black holes may enjoy two types of phase transition. We also find that there are three critical behaviors near the critical points for these black holes; nonphysical unstable to physical stable, large to small, and small to large black holes phase transition. Next, we employ a thermodynamical metric for studying thermodynamical geometry of these black holes. We show that the characteristic behavioral of Ricci scalar of this metric enables one to recognize the type of phase transition and critical behavior of the black holes near phase transition points. Finally, we will extend thermodynamical space by considering dilaton parameter as extensive parameter. We will show that by this consideration, Weinhold, Ruppeiner and Quevedo metrics provide extra divergencies which are not related to any phase transition point whereas our new method is providing an effective machinery.

hep-th↗

arXiv2015

Three dimensional nonlinear magnetic AdS solutions through topological defects

Inspired by large applications of topological defects in describing different phenomena in physics, and considering the importance of three dimensional solutions in AdS/CFT correspondence, in this paper we obtain magnetic anti-de Sitter solutions of nonlinear electromagnetic fields. We take into account three classes of nonlinear electrodynamic models; first two classes are the well-known BornInfeld like models including logarithmic and exponential forms and third class is known as the power Maxwell invariant nonlinear electrodynamics. We investigate the effects of these nonlinear sources on three dimensional magnetic solutions. We show that these asymptotical AdS solutions do not have any curvature singularity and horizon. We also generalize the static metric to the case of rotating solutions and find that the value of the electric charge depends on the rotation parameter. Finally, we consider the quadratic Maxwell invariant as a correction of Maxwell theory and in other words, we investigate the effects of nonlinearity as a correction. We study the behavior of the deficit angle in presence of these theories of nonlinearity and compare them with each other. We also show that some cases with negative deficit angle exists which are representing objects with different geometrical structure. We also show that in case of the static only magnetic field exists whereas by boosting the metric to rotating one, electric field appear too.

hep-th↗

arXiv2015

Thermodynamic stability of charged BTZ black holes: Ensemble dependency problem and its solution

Motivated by the wide applications of thermal stability and phase transition, we investigate thermodynamic properties of charged BTZ black holes. We apply the standard method to calculate the heat capacity and the Hessian matrix and find that thermal stability of charged BTZ solutions depends on the choice of ensemble. To overcome this problem, we take into account cosmological constant as a thermodynamical variable. By this modification, we show that the ensemble dependency is eliminated and thermal stability conditions are the same in both ensembles. Then, we generalize our solutions to the case of nonlinear electrodynamics. We show how nonlinear matter field modifies the geometrical behavior of the metric function. We also study phase transition and thermal stability of these black holes in context of both canonical and grand canonical ensembles. We show that by considering the cosmological constant as a thermodynamical variable and modifying the Hessian matrix, the ensemble dependency of thermal stability will be eliminated.

gr-qc↗

arXiv2015

Dilatonic Equation of Hydrostatic Equilibrium and Neutron Star Structure

In this paper, we present a new hydrostatic equilibrium equation related to dilaton gravity. We consider a spherical symmetric metric to obtain the hydrostatic equilibrium equation of stars in $4$-dimensions, and generalize TOV equation to the case of regarding a dilaton field. Then, we calculate the structure properties of neutron star using our obtained hydrostatic equilibrium equation employing the modern equations of state of neutron star matter derived from microscopic calculations. We show that the maximum mass of neutron star depends on the parameters of dilaton field and cosmological constant. In other words, by setting the parameters of new hydrostatic equilibrium equation, we calculate the maximum mass of neutron star.

gr-qc↗

arXiv2015

$P-V$ criticality and geometrothermodynamics of black holes with Born-Infeld type nonlinear electrodynamics

In this paper, we take into account the black hole solutions of Einstein gravity with logarithmic and exponential forms of nonlinear electrodynamics. We consider $Λ$ as a dynamical pressure to study the analogy of the black holes with the Van der Waals system. We plot P-v, T-v and G-T diagrams and investigate the phase transition of adS black holes in the canonical ensemble. We study the nonlinearity effects of electrodynamics and see how the power of nonlinearity affects critical behavior. We also investigate the effects of dimensionality on the critical values and analyze its crucial role. Moreover, we show the changes in the universal ratio P_{c}v_{c}/T_{c} for variation of different parameters. In addition, we make a comparison between linear and nonlinear electrodynamics and show that the lowest critical temperature belongs to Maxwell theory. Also, we make some arguments regarding to how power of nonlinearity brings the system to Schwarzschild-like and Reissner-Nordstrom-like limitations. Next, we study the critical behavior in context of heat capacity. We show that critical behavior of system is similar to one in phase diagrams of extended phase space. We point out that phase transition points of the extended phase space only appear as divergencies of heat capacity. We also extend the study of phase transitions through GTD method. We introduce two new metrics and show that divergencies of TRS of the new metrics coincide with phase transitions. The characteristic behavior of these divergencies, hence critical points is exactly the one that is obtained in extended phase space and heat capacity. We also introduce a new method for obtaining critical pressure and horizon radius by considering denominator of the heat capacity. We show that there are several benefits that make this approach favorable comparing to other ones.

gr-qc↗

arXiv2015

Extended phase space thermodynamics and $P-V$ criticality of charged black holes in Brans-Dicke theory

In this paper, taking in to account Brans-Dick theory, we investigate thermodynamic behavior of charged black hole solutions. We study the analogy of the black hole solution with the Van der Waals liquid-gas system in the extended phase space by considering the cosmological constant as dynamical pressure. We obtain critical values of thermodynamic coordinates and plot $P-r_{+}$ and $G-T$ diagrams to study the phase transition.

gr-qc↗

arXiv2015

Thermodynamic instability of topological black holes in Gauss-Bonnet gravity with a generalized electrodynamics

Motivated by the string corrections on the gravity and electrodynamics sides, we consider a quadratic Maxwell invariant term as a correction of the Maxwell Lagrangian to obtain exact solutions of higher dimensional topological black holes in Gauss-Bonnet gravity. We first investigate the asymptotically flat solutions and obtain conserved and thermodynamic quantities which satisfy the first law of thermodynamics. We also analyze thermodynamic stability of the solutions by calculating the heat capacity and the Hessian matrix. Then, we focus on horizon-flat solutions with adS asymptote and produce a rotating spacetime with a suitable transformation. In addition, we calculate the conserved and thermodynamic quantities for asymptotically adS black branes which satisfy the first law of thermodynamics. Finally, we perform thermodynamic instability criterion to investigate the effects of nonlinear electrodynamics in canonical and grand canonical ensembles.

gr-qc↗

arXiv2015

Third order Lovelock black branes in the presence of a nonlinear electromagnetic field

We consider third order Lovelock gravity coupled to an U(1) gauge field for which its Lagrangian is given by a power of Maxwell invariant. In this paper, we present a class of horizon flat rotating black branes and investigate their geometrical properties and the effect of nonlinearity on the solutions. We use some known formulas and methods to calculate thermodynamic and conserved quantities. Finally, we check the satisfaction of the first law of thermodynamics.

gr-qc↗

arXiv2015

Thermodynamic instability of topological black holes with nonlinear source

In this paper, we obtain higher dimensional topological black hole solutions of Einstein-$Λ$ gravity in the presence of a class of nonlinear electrodynamics. First, we calculate the conserved and thermodynamic quantities of ($n+1$)-dimensional asymptotically flat solutions and show that they satisfy the first law of thermodynamics. Also, we investigate the stability of these solutions in the (grand) canonical ensemble. Second, we endow a global rotation to the static Ricci-flat solutions and calculate the conserved quantities of solutions by using the counterterm method. We obtain a Smarr-type formula for the mass as a function of the entropy, the angular momenta and the electric charge, and show that these quantities satisfy the first law of thermodynamics. Then, we perform a stability analysis of the rotating solutions both in the canonical and the grand canonical ensembles.

gr-qc↗