arXiv subjects

S. H. Hendi

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

At least 55 records · Page 3Linked to original sources

arXiv2017

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 thermodynamical properties are modified. To have better picture regarding the phase transitions, the concept of the extended phase space is employed. It will be shown that in the absence of the electric field, magnetic black holes present van der Waals like phase transition. Furthermore, it will be highlighted that for super magnetized black holes, no phase transition exists.

gr-qc↗

arXiv2017

Dilatonic black holes in gravity's rainbow with a nonlinear source: the effects of thermal fluctuations

This paper is devoted to investigate nonlinearly charged dilatonic black holes in the context of gravity's rainbow with two cases: I) by considering the usual entropy, II) in the presence of first order logarithmic correction of entropy. First, exact solutions of dilatonic Born-Infeld gravity with an energy dependent Liouville-type potential with black hole interpretation are obtained. Then, thermodynamic properties of the mentioned cases are studied, separately. It will be shown that although mass, entropy and heat capacity are modified due to the presence of first order correction, the temperature remains independent of it. Furthermore, it will be shown that divergencies of the heat capacity, hence phase transition points are also independent of first order correction whereas the stability conditions are highly sensitive to variation of the correction parameter. Except for the effects of first order correction, we will also draw a limit on values of the dilatonic parameter and show that it is possible to recognize AdS and dS thermodynamical behaviors for two specific branches of the dilatonic parameter. In addition, the effects of nonlinear electromagnetic field and energy functions on thermodynamical behavior of the solutions will be highlighted and dependency of critical behavior, on these generalizations will be investigated.

gr-qc↗

arXiv2017

Expansion of magnetic neutron stars in an energy (in)dependent spacetime

Regarding the strong magnetic field of neutron stars and high energy regime scenario which is based on high curvature region near the compact objects, one is motivated to study magnetic neutron stars in an energy dependent spacetime. In this paper, we show that such strong magnetic field and energy dependency of spacetime have considerable effects on the properties of neutron stars. We examine the variations of maximum mass and related radius, Schwarzschild radius, average density, gravitational redshift, Kretschmann scalar and Buchdahl theorem due to magnetic field and also energy dependency of metric. First, it will be shown that the maximum mass and radius of neutron stars are increasing function of magnetic field while average density, redshift, the strength of gravity and Kretschmann scalar are decreasing functions of it. These results are due to a repulsive-like force behavior for the magnetic field. Next, the effects of the gravity's rainbow will be studied and it will be shown that by increasing the rainbow function, the neutron stars could enjoy an expansion in their structures. Then, we obtain a new relation for the upper mass limit of a static spherical neutron star with uniform density in gravity's rainbow (Buchdahl limit) in which such upper limit is modified as $M_{eff}<\frac{4c^{2}R}{9G}$. In addition, stability and energy conditions for the equation of state of neutron star matter are also investigated and a comparison with empirical results is done. It is notable that the numerical study in this paper is conducted by using the lowest order constrained variational (LOCV) approach in the presence of magnetic field employing AV18 potential.

gr-qc↗

arXiv2017

Neutron stars structure in the context of massive gravity

Motivated by the recent interests in spin$-2$ massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in $4$ and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV$18$ potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

gr-qc↗

arXiv2017

Black holes in massive gravity as heat engines

The paper at hand studies the heat engine provided by black holes in the presence of massive gravity. The main motivation is to investigate the effects of massive gravity on different properties of the heat engine. It will be shown that massive gravity parameters and graviton's mass modify the efficiency of engine on a significant level. Furthermore, it will be shown that it is possible to have the heat engine for non-spherical black holes in massive gravity and we study the effects of topological factor on properties of the heat engine. Surprisingly, it will be shown that the highest efficiency for the heat engine belongs to black holes with hyperbolic horizon, while the lowest one belongs to spherical black holes.

hep-th↗

arXiv2017

Geometrical thermodynamics and P-V criticality of the black holes with power-law Maxwell field

We study thermodynamical structure of Einstein black holes in the presence of power Maxwell invariant nonlinear electrodynamics for two different cases. The behavior of the temperature and conditions regarding the stability of these black holes are investigated. Since the language of geometry is an effective method in general relativity, we concentrate on the geometrical thermodynamics to build a phase space for studying phase transition. In addition, taking into account the denominator of the heat capacity, we use the proportionality between cosmological constant and thermodynamical pressure to extract the critical values for these black holes. Besides, the effects of the variation of different parameters on thermodynamical structure of these black holes are investigated. In addition, some thermodynamical properties such as volume expansion coefficient, speed of sound and isothermal compressibility coefficient are calculated and some remarks regarding these quantities are given.

hep-th↗

arXiv2017

Traversable asymptotically flat wormholes in Rastall gravity

There are some gravitational theories in which the ordinary energy-momentum conservation law is not valid in the curved spacetime. Rastall gravity is one of the known theories in this regard which includes a non-minimal coupling between geometry and matter fields. Equipped with the basis of such theory, we study the properties of traversable wormholes with flat asymptotes. We investigate the possibility of exact solutions by a source with the baryonic matter state parameter. Our survey indicates that Rastall theory has considerable effects on the wormhole characteristics. In addition, we study various case studies and show that the weak energy condition may be met for some solutions. We also give a discussion regarding to traversability of such wormhole geometry with phantom sources.

gr-qc↗

arXiv2017

Charged BTZ black holes in the context of massive gravity's rainbow

BTZ black holes are excellent laboratories for studying black hole thermodynamics which is a bridge between classical general relativity and quantum nature of gravitation. In addition, three-dimensional gravity could have equipped us for exploring some of the ideas behind the two dimensional conformal field theory based on the $AdS_{3}/CFT_{2}$. Considering the significant interests in these regards, we examine charged BTZ black holes. We consider the system contains massive gravity with energy dependent spacetime to enrich the results. In order to make high curvature (energy) BTZ black holes more realistic, we modify the theory by energy dependent constants. We investigate thermodynamic properties of the solutions by calculating heat capacity and free energy. We also analyze thermal stability and study the possibility of Hawking-Page phase transition. At last, we study geometrical thermodynamics of these black holes and compare the results of various approaches.

hep-th↗

arXiv2017

Topological charged black holes in massive gravity's rainbow and their thermodynamical analysis through various approaches

Violation of Lorentz invariancy in the high energy quantum gravity motivates one to consider an energy dependent spacetime with massive deformation of standard general relativity. In this paper, we take into account an energy dependent metric in the context of a massive gravity model to obtain exact solutions. We investigate the geometry of black hole solutions and also calculate the conserved and thermodynamic quantities, which are fully reproduced by the analysis performed with the standard techniques. After examining the validity of the first law of thermodynamics, we conduct a study regarding the effects of different parameters on thermal stability of the solutions. In addition, we employ the relation between cosmological constant and thermodynamical pressure to study the possibility of phase transition. Interestingly, we will show that for the specific configuration considered in this paper, van der Waals like behavior is observed for different topology. In other words, for flat and hyperbolic horizons, similar to spherical horizon, a second order phase transition and van der Waals like behavior are observed. Furthermore, we use geometrical method to construct phase space and study phase transition and bound points for these black holes. Finally, we obtain critical values in extended phase space through the use of a new method.

gr-qc↗

arXiv2017

Dilatonic BTZ black holes with power-law field

Motivated by low energy effective action of string theory and large applications of BTZ black holes, we will consider minimal coupling between dilaton and nonlinear electromagnetic fields in three dimensions. The main goal is studying thermodynamical structure of black holes in this set up. Temperature and heat capacity of these black holes are investigated and a picture regarding their phase transitions is given. In addition, the role and importance of studying the mass of black holes is highlighted. We will see how different parameters modify thermodynamical quantities, hence thermodynamical structure of these black holes. In addition, geometrical thermodynamics is used to investigate thermodynamical properties of these black holes. In this regard, the successful method is presented and the nature of interaction around bound and phase transition points is studied.

gr-qc↗

arXiv2017

Black hole thermodynamics in Lovelock gravity's rainbow with (A)dS asymptote

In this paper, we combine Lovelock gravity with gravity's rainbow to construct Lovelock gravity's rainbow. Considering the Lovelock gravity's rainbow coupled to linear and also nonlinear electromagnetic gauge fields, we present two new classes of topological black hole solutions. We compute conserved and thermodynamic quantities of these black holes (such as temperature, entropy, electric potential, charge and mass) and show that these quantities satisfy the first law of thermodynamics. In order to study the thermal stability in canonical ensemble, we calculate the heat capacity and determinant of the Hessian matrix and show in what regions there are thermally stable phases for black holes. Also, we discuss the dependence of thermodynamic behavior and thermal stability of black holes on rainbow functions. Finally, we investigate the critical behavior of black holes in the extended phase space and study their interesting properties.

hep-th↗

arXiv2017

van der Waals like behaviour of topological AdS black holes in massive gravity

Motivated by recent developments in black hole thermodynamics, we investigate van der Waals phase transitions of charged black holes in massive gravity. We find that massive gravity theories can exhibit strikingly different thermodynamic behaviour compared to that of Einstein gravity, and that the mass of the graviton can generate a range of new phase transitions for topological black holes that are otherwise forbidden.

gr-qc↗

arXiv2017

Neutron stars in Einstein-$Λ$ gravity: the cosmological constant effects

Regarding a $d-$dimensional spherically symmetric line element in the context of Einstein-$Λ$ gravity, the hydrostatic equilibrium equation of stars is obtained. Then, by using the lowest order constrained variational (LOCV) method with the AV$18$ potential and employing microscopic many body calculations in the modern equation of state, the structure properties of neutron stars are investigated. Regardless of cosmological point of view and considering arbitrary positive and negative values of the cosmological constant, the maximum mass of the neutron stars and their corresponding radius in $4$-dimensions are computed. The results show that there is an upper limit for the maximum mass of neutron star for positive cosmological constant ($M_{\max }\leq 1.68M_{\odot }$). On the other hand, it is shown that the Einstein gravity cannot explain the structure of neutron star with negative $Λ$. Other properties of neutron stars such as; the Schwarzschild radius, average density, compactness and Buchdahl- Bondi bound are studied. In addition, by using the Buchdahl-Bondi bound for neutron stars, stability of these stars is investigated. Finally, the dynamical stability is investigated and shown that the neutron stars follow the dynamical stability in this gravity.

gr-qc↗

arXiv2017

Phase transition of charged black holes in massive gravity through new methods

Motivated by providing preliminary steps to understand the conception of quantum gravity, in this paper, we study the phase structure of a semiclassical gravitational system. We investigate the stability conditions and phase transition of charged black holes in massive gravity via canonical and geometrical thermodynamic approaches. We point out the effects of massive parameter on stability conditions of these black holes and show how massive coefficients affect the phase transition points of these black holes. We also study the effects of boundary topology on thermodynamical behavior of the system. In addition, we give some arguments regarding the role of higher dimensions and highlight the effect of the electric charge in thermodynamical behavior. Then, we extend our study to geometrical thermodynamic approach and show that it can be a successful method for studying the black hole phase transition. At last, by employing the relation between thermodynamical pressure and cosmological constant, critical behavior of the system and the effects of different parameters on critical values are investigated.

hep-th↗

arXiv2017

Thermodynamical Structure of AdS Black Holes in Massive Gravity with Stringy Gauge-Gravity Corrections

Motivated by gauge/gravity group in the low energy effective theory of the heterotic string theory and novel aspects of massive gravity in the context of lattice physics, the minimal coupling of Gauss-Bonnet-massive gravity with Born-Infeld electrodynamics is considered. At first, the metric function is calculated and then the geometrical properties of the solutions are investigated. It is found that there is an essential singularity at the origin and the intrinsic curvature is regular elsewhere. In addition, the effects of massive parameters are studied and black hole solutions with multi horizons are found in this gravity. Also the conserved and thermodynamic quantities are calculated, and it is shown that the solutions satisfy the first law of thermodynamics. Furthermore, using heat capacity of these black holes, thermal stability and phase transitions are investigated. The variation of different parameters and related modifications on the (number of) phase transition are examined. Next, the critical behavior of the Gauss-Bonnet-Born-Infeld-massive black holes in the context of extended phase space is studied. It is shown that how the variation of the different parameters affects the existence and absence of phase transition. Also, it is found that for specific values of different parameters, these black holes may enjoy the existence of new type of phase transition which to our knowledge was not observed in black hole physics before.

hep-th↗

arXiv2016

Nonlinearly charged dilatonic black holes and their Brans-Dicke counterpart: Energy dependent spacetime

Regarding the wide applications of dilaton gravity in the presence of electrodynamics, we introduce a suitable Lagrangian for the coupling of dilaton with gauge field. There are various Lagrangians which show the coupling between scalar fields and electrodynamics with correct special situations. In this paper, taking into account conformal transformation of Brans-Dicke theory with an electrodynamics Lagrangian, we show that how scalar field should couple with electrodynamics in dilaton gravity. In other words, in order to introduce a correct Lagrangian of dilaton gravity, one should check at least two requirements: compatibility with Brans-Dicke theory and appropriate special situations. Finally, we apply the mentioned method to obtain analytical solutions of dilaton-Born-Infeld and Brans-Dicke-Born-Infeld theories with energy dependent spacetime.

gr-qc↗

arXiv2016

Modified TOV in gravity's rainbow: properties of neutron stars and dynamical stability conditions

In this paper, we consider a spherical symmetric metric to extract the hydrostatic equilibrium equation of stars in $(3+1)-$dimensional gravity's rainbow in the presence of cosmological constant. Then, we generalize the hydrostatic equilibrium equation to $d$-dimensions and obtain the hydrostatic equilibrium equation for this gravity. Also, we obtain the maximum mass of neutron star using the modern equations of state of neutron star matter derived from the microscopic calculations. It is notable that, in this paper, we consider the effects of rainbow functions on the diagrams related to the mass-central mass density ($M$-$ρ_{c}$) relation and also the mass-radius ($M$-$R$) relation of neutron star. We also study the effects of rainbow functions on the other properties of neutron star such as the Schwarzschild radius, average density, strength of gravity and gravitational redshift. Then, we apply the cosmological constant to this theory to obtain the diagrams of $M$-$ρ_{c}$ (or $M$-$R$) and other properties of these stars. Next, we investigate the dynamical stability condition for these stars in gravity's rainbow and show that these stars have dynamical stability. We also obtain a relation between mass of neutron stars and Planck mass. In addition, we compare obtained results of this theory with the observational data.

hep-th↗

arXiv2016

F(R) gravity's rainbow and its Einstein counterpart

Motivated by UV completion of general relativity with a modification of a geometry at high energy scale, it is expected to have an energy dependent geometry. In this paper, we introduce charged black hole solutions with power Maxwell invariant source in the context of gravity's rainbow. In addition, we investigate two classes of $F(R)$ gravity's rainbow solutions. At first, we study energy dependent $F(R)$ gravity without energy momentum tensor, and then we obtain $F(R)$ gravity's rainbow in the presence of conformally invariant Maxwell source. We study geometrical properties of the mentioned solutions and compare their results. We also give some related comments regarding to thermodynamical behavior of the obtained solutions and discuss thermal stability of the solutions.

gr-qc↗