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In this paper, a modified version of the hydrostatic equilibrium equation based on the mimetic gravity in the presence of perfect fluid is revisited. By using the different known equation of states, the structural properties of neutron stars are investigated in general relativity and mimetic gravity. Comparing the obtained results, we show that, unlike general relativity, we can find the appropriate equation of states that support observational data in the context of mimetic gravity. We also find that the results of relativistic mean-field-based models of the equation of states are in better agreement with observational data than non-relativistic models., 19 pages, 9 figures

A new spherically symmetric exact solution of Einstein gravity in the presence of a nonlinear electromagnetic field is introduced. It is shown that such a solution can be interpreted as an electrically charged regular black hole that behaves like Reissner−Nordstrom metric, asymptotically. An extension of the solution in the presence of cosmological constant is presented and thermodynamic properties of the solution are studied in the extended phase space thermodynamics. Then, thermal stability and possible phase transition are investigated and the van der Waals like behavior is observed. Finally, the relation between the photon sphere with a thermodynamic phase transition is studied.

Regarding the advanced robotic technology, one of the logical questions is the human roles in controlling observation devices which may affect the results of data. Here, we want to study the light curves of robotic telescopes and then compare it with a non-robotic one to find out the influence of technology/human on data accuracy.

Investigation of changes in the light of a binary star with plotted light curves, which shows the variation of light during a periodic time, helps us to obtain useful information about the binary systems. In this article, by R-band photometric light curve modeling of BN Ari binary star (in 2015) which is located in Aries constellation, we plot related light curve, obtain new period for the system and calculate the rate of period changes. We also calculate a new ephemeris of such system by fitting a quadratic curve to the O–C values. Finally, we use the Wilson–Devinney code as implemented in the PHOEBE to simulate such a system, and obtain its specific geometrical and physical parameters.

Considering the variable cosmological constant in the extended phase space has a significant background in the black hole physics. It was shown that the thermodynamic behavior of charged AdS black hole surrounded by the quintessence in the extended phase space is similar to the van der Waals fluid. In this paper, we indicate that such a black hole admits the same criticality and van der Waals like behavior in the non-extended phase space. In other words, we keep the cosmological constant as a fixed parameter, and instead, we consider the normalization factor as a thermodynamic variable. We show that there is a first-order small/large black hole phase transition which is analogous to the liquid/gas phase transition in fluids. We introduce a new picture of the equation of state and then we calculate the corresponding critical quantities. Moreover, we obtain the critical exponents and show that they are the same values as the van der Waals system. Finally, we study the photon sphere and the shadow observed by a distant observer and investigate how the shadow radius may be affected by the variation of black hole parameters. We also investigate the relations between shadow radius and phase transitions and calculate the critical shadow radius where the black hole undergoes a second-order phase transition., Comment: 25 pages, 14 figures

Recently, the action growth rate of a variety of four-dimensional regular magnetic black holes in F frame is obtained in [1]. Here, we study the action growth rate of a four-dimensional regular electric black hole in P frame that is the Legendre transformation of F frame. We also investigate the action growth rates of the Wheeler-De Witt patch for such black hole configurations at the late time and examine the Lloyd bound on the rate of quantum computation. We show that although the form of the Lloyd bound formula remains unaltered, the energy modifies due to a non-vanishing trace of the energy-momentum tensor and some extra terms may appear in the total growth action. We also investigate the asymptotic behavior of complexity in two conjectures for static and rotating regular black holes., 26 pages, 13 figures

In this paper, we first investigate the thermal stability of black holes in conformal Weyl gravity with a comparison with the Schwarzschild black holes. Then, we consider a minimally coupled massive scalar perturbation and calculate the quasinormal modes in asymptotically dS spacetime by employing the sixth order WKB approximation and asymptotic iteration method. The deviations from those of the Schwarzschild-dS solutions are obtained and the possibility of the presence of quasi-resonance modes for Weyl black hole solutions is investigated. Finally, we consider a massless scalar perturbation in the background of asymptotically AdS solutions and calculate the quasinormal modes by using the pseudospectral method. The effects of the free parameter of the theory on the quasinormal modes are studied and deviations from those of the Schwarzschild-AdS black holes are investigated. The imaginary part of quasinormal frequencies in AdS spacetime is the time scale of a thermal state (in the conformal field theory) to approach thermal equilibrium., 16 pages with 8 captioned figures and 5 tables. Published version

Recently, there has been a surge of interest in the 4D Einstein-Gauss-Bonnet (4D EGB) gravity theory which bypasses the Lovelock theorem and avoids Ostrogradsky's instability. Such a novel theory has nontrivial dynamics and presents several predictions for cosmology and black hole physics. Motivated by recent astrophysical observations and the importance of anti-de Sitter spacetime, we investigate shadow geometrical shapes and deflection angle of light from the charged AdS black holes in 4D EGB gravity theory. We explore the shadow behaviors and photon sphere around such black holes, and inspect the effect of different parameters on them. Then, we present a study regarding the energy emission rate of such black holes and analyze the significant role of the Gauss-Bonnet (GB) coupling constant in the radiation process. Then, we perform a discussion of holographic heat engines of charged 4D EGB-AdS black holes by obtaining the efficiency of a rectangular engine cycle. Finally, by comparing heat engine efficiency with the Carnot efficiency, we indicate that the ratio $\frac{\eta }{\eta_{c}}$ is always less than one which is consistent with the thermodynamic second law., Comment: 14 pages, 7 figures

Motivated by the investigation of a black hole’s properties in the lab, some interesting subjects such as analogue gravity and transformation optics are generated. In this paper, we look for analogies between the geometry of a gravitating system and the optical medium. In addition, we recognize that appropriate two-dimensional metamaterials can be used to mimic the propagation of light in the curved spacetimes and behave like black holes which are incident with light rays in the equatorial plane. The resemblance of metamaterials with Kerr and Reissner–Nordström spacetimes is studied. Finally, we compare the results of two-dimensional simulation for light propagation in the corresponding two-dimensional metamaterials with those obtained from the geometrical optical limit.

Respecting the angular momentum conservation of torque-free systems, it is natural to consider rotating solutions of massive objects. Besides that, motivated by the realistic astrophysical black holes that rotate, we use the Newman-Janis formalism to construct a regular rotating black hole. We start with a nonlinearly charged regular static black hole in the framework of the standard general relativity and then obtain the associated rotating solution through such a formalism. We investigate the geometrical properties of the metric by studying the boundary of ergosphere. We also analyze thermodynamic properties of the solution in AdS spacetime and examine thermal stability and possible phase transition. In addition, we perturb the black hole by using of a real massless scalar field as a probe to investigate its dynamic stability. We obtain an analytic expression for the real and imaginary parts of the quasinormal frequencies. Finally, we look for a connection between the quasinormal frequencies and the properties of the photon sphere in the eikonal limit., 19 pages, 14 figures

In order to classify and understand the spacetime structure, investigation of the geodesic motion of massive and massless particles is a key tool. So the geodesic equation is a central equation of gravitating systems and the subject of geodesics in the black hole dictionary attracted much attention. In this paper, we give a full description of geodesic motions in three-dimensional spacetime. We investigate the geodesics near charged BTZ black holes and then generalize our prescriptions to the case of massive gravity. We show that electric charge is a critical parameter for categorizing the geodesic motions of both lightlike and timelike particles. In addition, we classify the type of geodesics based on the particle properties and geometry of spacetime., Comment: 26 pages with 15 captioned figures

In this paper, we study an extended phase space thermodynamics of a nonlinearly charged AdS black hole. We examine both the local and global stabilities, and possible phase transition of the black hole solutions. Finally, we compute quasi-normal modes via scalar perturbations and compare the obtained results with those of RN-AdS black hole., Comment: 17 pages with 15 captioned figures. Published in EPJC

Regarding a special class of pure F(R) gravity in three dimensions, we obtain, analytically, Lifshitz-like black hole solutions. We check the geometrical properties of the solutions which behave such as charged BTZ black holes in special limit. We also investigate the thermodynamic properties of the solutions and examine the first law of thermodynamics and Smarr formula. In addition, we study thermal stability via the heat capacity and discuss the possibility of criticality in the extended phase space., Comment: 8 pages with 2 captioned figures. Accepted in Physics Letters B

Massive gravities in anti-de Sitter spacetime can be viewed as effective dual field theories of different phases of condensed matter systems with broken translational symmetry such as solids, (perfect) fluids, and liquid crystals. Motivated by this fact, we explore the black hole chemistry (BHC) of these theories and find a new range of novel phase transitions close to realistic ones in ordinary physical systems. We find that the equation of state of topological black holes (TBHs) at their inflection point(s) in $d$-dimensional spacetime reduces to a polynomial equation of degree $(d-4)$, which yields up to $n=(d-4)$ critical points. As a result, for (neutral) TBHs, we observe triple-point phenomena with the associated first-order phase transitions (in $d \ge 7$), and a new phenomenon we call an $N$-fold reentrant phase transition, in which several ($N$) regions of thermodynamic phase space exhibit distinct reentrant phase transitions, with associated virtual triple points and zeroth-order phase transitions (in $d \ge 8$), as well as Van der Waals transitions (in $d \ge 5$) and reentrant (in $d \ge 6$) behavior. We conclude that BHC in higher-dimensional massive gravity is very likely to offer further new surprises., Comment: 7 pages, 3 figures, published version

It is known that scalar-tensor gravity models can be studied in Einstein and Jordan frames. In this paper, we consider a model of scalar-tensor gravity in Einstein's frame to calculate the Lifshitz-like black hole solutions with different horizon topologies. We study thermodynamic properties and first order van der Waals like phase transition, and find that the Lifshitz parameter affects the phase structure. In addition, we investigate thermal stability by using the behavior of heat capacity and various methods of geometrical thermodynamics., Comment: 13 pages with 8 captioned figures. Accepted for publication in AdP

In the context of Black Hole Chemistry (BHC), holographic phase transitions of asymptotically anti-de Sitter (AdS) charged topological black holes (TBHs) in massive gravity coupled to Power Maxwell Invariant (PMI) electrodynamics are discussed in the grand canonical (fixed $U(1)$ potential, $\Phi$) ensemble. Considering all higher-order graviton's self-interactions of (dRGT) massive gravitational field theory in arbitrary dimensions, exact TBH solutions are derived, the explicit form of the on-shell action is computed, and the associated thermodynamic quantities in the Grand Canonical Ensemble (GCE) are calculated. In addition, the validity of the first law of thermodynamics and Smarr relation are examined in the extended phase space. Regarding this model, it is shown that a van der Waals (vdW) behavior takes place in $d \ge 4$ dimensions, a typical reentrant phase transition is observed in $d \ge 5$, and both anomalous vdW and triple point phenomena are recognized in $d \ge 6$. So, the results are quite different from their counterparts in the GCE of Maxwell-massive gravity. Besides, we briefly study the critical behaviors of higher-dimensional TBHs with a conformally invariant Maxwell source as a special subgroup of our solutions for both Einstein and massive gravity theories in various ensembles., Comment: 21 pages, 4 figures, 2 tables - Published version

In this paper, we work on the topological Lifshitz-like black hole solutions of a special class of vacuum $F(R)-$gravity that are static and spherically symmetric. We investigate geometric and thermodynamic properties of the solutions with due respect to the validity of the first law of thermodynamics. We examine the van der Waals like behavior for asymptotically AdS solutions with spherical horizon by studying the $P-v$, $G-T$ and $C_{Q,P}-r_{+}$ diagrams and find a consistent result. We also investigate the same behavior for hyperbolic horizon and interestingly find that the system under study can experience a phase transition with negative temperature., 14 pages with 7 captioned figures. Some additional notes are added. Accepted in EPJC

Stability criteria of nearly extreme black holes in the perturbations level is one of the interesting issues in gravitational systems. Considering the nearly extreme conformal-de Sitter black holes, in this paper, we obtain an exact relation for the quasinormal modes of scalar perturbations. As for stability criteria, we find a lower bound on the event horizon radius which is corresponding to an upper bound on the value of the quasinormal frequencies. In addition, we show that the asymptotic behavior of quasinormal modes gives highly damped modes which is important due to possible connection between their real part and the Barbero-Immirzi parameter. We also obtain the Lyapunov exponent and the angular velocity of unstable circular null geodesics. Finally, we examine the validity of the relation between calculated quasinormal modes and unstable circular null geodesics., 9 pages with one captioned figure and a table. Accepted in PRD

In this work, a correspondence between black hole solutions of conformal and massive theories of gravity is found. It is seen that this correspondence imposes some constraints on parameters of these theories. What is more, a relation between the mass of black holes and the parameters of massive gravity is found. Indeed, the acceptable ranges of massive gravity parameters ($c_{1}$\ and $c_{2}$) are found. It is shown that by considering the positive mass of black holes, some ranges of $c_{1}$\ and $c_{2}$ are acceptable., 7 pages, 1 figure

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. © 2016 The Author(s), Research Institute for Astronomy and Astrophysics of Maragha

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.

It was shown that with the combination of three Liouville-type dilaton potentials, one can derive dilaton black holes in the background of anti-de-Sitter (AdS) spaces. In this paper, we further extend the study on the dilaton AdS black holes by investigating their thermodynamic instability through a geometry approach. First, we review thermodynamic quantities of the solutions and check the validity of the first law of thermodynamics. Then, we investigate phase transitions and stability of the solutions. In particular, we disclose the effects of the dilaton field on the stability of the black holes. We also employ the geometrical approach toward thermodynamical behavior of the system and find that the divergencies in the Ricci scalar coincide with roots and divergencies in the heat capacity. We find that the behavior of the Ricci scalar around divergence points depends on the type of the phase transition. © 2016 Published by NRC Research Press., Research Institute for Astronomy and Astrophysics of Maragha Shiraz Institute for Cancer Research, Shiraz University of Medical Sciences

Considering the advantages of two independent nonlinear electrodynamic models, we are going to combine them to obtain a unified theory. Taking into account the functional form of both the Born–Infeld and conformally invariant Maxwell Lagrangians, we use the composition method of two arbitrary functions F(x) and G(x) ( $$FoG(x)=F(G(x))$$ and $$GoF(x)=G(F(x))$$ ) to obtain a new nonlinear Lagrangian. We obtain an electric field related to this new Lagrangian by solving a nonlinear differential equation. The numerical results are in excellent agreement with the analytical solutions in special limits and we expect that our numerical code precisely predict the behavior of the electric field for more general cases.

The recent reported gravitational wave detection motivates one to investigate the properties of different black hole models, especially their behavior under (axial) gravitational perturbation. Here, we study the quasinormal modes of black holes in Weyl gravity. We derive the master equation describing the quasinormal radiation by using a relation between the Schwarzschild-anti de Sitter black holes and Weyl solutions, and also the conformal invariance property of the Weyl action. It will be observed that the quasinormal mode spectra of the Weyl solutions deviate from those of the Schwarzschild black hole due to the presence of an additional linear $r$-term in the metric function. We also consider the evolution of the Maxwell field on the background spacetime and obtain the master equation of electromagnetic perturbations. Then, we use the WKB approximation and asymptotic iteration method to calculate the quasinormal frequencies. Finally, the time evolution of modes is studied through the time-domain integration of the master equation., Comment: 15 pages with 3 captioned figures. Published version

In this paper, we investigate thermodynamical structure of dyonic black holes in the presence of gravity's rainbow. We confirm that for super magnetized and highly pressurized scenarios, the number of black holes’ phases is reduced to a single phase. In addition, due to specific coupling of rainbow functions, it is possible to track the effects of temporal and spatial parts of our setup on thermodynamical quantities/behaviors including equilibrium point, existence of multiple phases, possible phase transitions and conditions for having a uniform stable structure. © 2018 The Authors, Research Institute for Astronomy and Astrophysics of Maragha

Considering de Rham-Gabadadze-Tolley theory of massive gravity coupled with (ghost free) higher curvature terms arisen from the Lovelock Lagrangian, we obtain charged AdS black hole solutions in diverse dimensions. We compute thermodynamic quantities in the extended phase space by considering the variations of the negative cosmological constant, Lovelock coefficients ($\alpha_{i}$) and massive couplings ($c_{i}$), and prove that such variations is necessary for satisfying the extended first law of thermodynamics as well as associated Smarr formula. In addition, by performing a comprehensive thermal stability analysis for the topological black hole solutions, we show in what regions thermally stable phases exist. Calculations show the results are radically different from those in Einstein gravity. Furthermore, we investigate $P-V$ criticality of massive charged AdS black holes in higher dimensions, including the effect of higher curvature terms and massive parameter, and find that the critical behavior and phase transition can happen for non-compact black holes as well as spherically symmetric ones. The phase structure and critical behavior of topological AdS black holes are drastically restricted by the geometry of event horizon. In this regard, the universal ratio, i.e. $\frac{{{P_c}{v_c}}}{{{T_c}}}$, is a function of the event horizon topology. It is shown the phase structure of AdS black holes with non-compact (hyperbolic) horizon could give birth to three critical points corresponds to a reverse van der Waals behavior for phase transition which is accompanied with two distinct van der Waals phase transitions. For black holes with spherical horizon, the van der Waals, reentrant and analogue of solid/liquid/gas phase transitions are observed., Comment: 36 pages, 22 Figures

Quantum fluctuation effects have an irrefutable role in high-energy physics. Such fluctuation can be often regarded as a correction of the infrared (IR) limit. In this paper, the effects of the first-order correction of entropy, caused by thermal fluctuation, on the thermodynamics of charged black holes in gravity's rainbow will be discussed. It will be shown that such correction has profound contributions to the high-energy limit of thermodynamical quantities and the stability conditions of black holes, and, interestingly, has no effect on thermodynamical phase transitions. The coupling between gravity's rainbow and the first-order correction will be addressed. In addition, the measurement of entropy as a function of fluctuation of temperature will be covered, and it will be shown that the de Sitter case enforces an upper limit on the values of temperature and produces cyclic-like diagrams, while for the anti-de Sitter case, a lower limit on the entropy is provided; although for special cases a cyclic-like behavior could be observed, no upper or lower limit exists for the temperature. In addition, a comparison between non-correction and correction-included cases on the thermodynamical properties of solutions will also be discussed and the effects of the first-order correction will be highlighted. It will be shown that the first-order correction provides solutions with larger classes of thermal stability conditions, which may result in the existence of a larger number of thermodynamical structures for the black holes. © The Author(s) 2018. Published by Oxford University Press on behalf of the Physical Society of Japan., Research Institute for Astronomy and Astrophysics of Maragha

In this paper, we propose a n-dimensional action in which gravity is coupled to exponential nonlinear electrodynamics and scalar dilaton field with Liouville-type potential. By varying the action, we obtain the field equations. Then, we construct a new class of charged, rotating black brane solutions, with k = [(n-1)/2] rotation parameters, of this theory. Because of the presence of the Liouville-type dilaton potential, the asymptotic behavior of the obtained solutions is neither flat nor (anti)-de Sitter. We investigate the causal structure of the space-time in ample details. We find the suitable counter term that removes the divergences of the action in the presence of the dilaton field, and calculate the conserved and thermodynamic quantities of the space-time. Interestingly enough, we find that the conserved quantities crucially depend on the dilaton coupling constant, ?, while they are independent of the nonlinear parameter, ß. We also check the validity of the first law of thermodynamics on the black brane horizon. Finally, we study thermal stability of the solutions by computing the heat capacity in the canonical ensemble. We disclose the effects of rotation parameter, nonlinearity of electrodynamics, and dilaton field on the thermal stability conditions. © 2015 Published by NRC Research Press.

Motivated by considerable interests of Myers-Perry black holes, we employ the perturbative method to obtain a family of extremal charged rotating black hole solutions in odd dimensional Einstein-Born-Infeld-dilaton gravity. We start with an extremal Myers-Perry black hole with equal angular momenta, and then by adding the dilaton field and the nonlinear Born-Infeld electrodynamics, we find an extremal nonlinearly charged rotating black holes. The perturbative parameter is assumed to be the electric charge q and the perturbations are performed up to the third order. We then study the physical properties of these Born-Infeld-dilaton black holes. In particular, we show that the perturbative parameter, q, the dilaton coupling constant, ?, and the Born-Infeld parameter, ß, modify the Smarr formula and the values of the gyromagnetic ratio of the extremal charged rotating black holes. © 2015 Elsevier Inc., Common Fund for Commodities

We construct a new class of asymptotically (a)dS black hole solutions of Einstein-Yang-Mills massive gravity in the presence of Born-Infeld nonlinear electrodynamics. The obtained solutions possess a Coulomb electric charge, massive term and a non-abelian hair as well. We calculate the conserved and thermodynamic quantities, and investigate the validity of the first law of thermodynamics. Also, we investigate thermal stability conditions by using the sign of heat capacity through canonical ensemble. Next, we consider the cosmological constant as a thermodynamical pressure and study the van der Waals like phase transition of black holes in the extended phase space thermodynamics. Our results indicate the existence of a phase transition which is affected by the parameters of theory. Finally, we consider a massless scalar perturbation in the background of asymptotically adS solutions and calculate the quasinormal modes by employing the pseudospectral method. The imaginary part of quasinormal frequencies is the time scale of a thermal state (in the conformal field theory) for the approach to thermal equilibrium., Comment: 21 pages and 7 figures. Published version

The motion of a point charged particle moving in the background of the critical power Maxwell charged AdS black holes in a probe approximation is studied. The extended phase space, where the cosmological constant appears as a pressure, is regarded and the effective potential is investigated. At last, the mass-to-charge ratio and the large q limit are studied. © 2018 American Physical Society., Research Institute for Astronomy and Astrophysics of Maragha

The possibility of a nonzero graviton mass has been widely pursued in the literature. In this work we investigate a black hole solution in massive gravity with a degenerate fiducial metric often used in the literature. We find that the end state of Hawking evaporation leads to black hole remnant, which could help to ameliorate the information paradox. We prove that these remnants only exist in anti-de Sitter spacetime. Nevertheless, we speculate on their possible relevance to our Universe as dark matter candidate, in view of the possibility that our Universe could be inherently anti-de Sitter-like, with a transient accelerated expansion phase., Comment: version accepted for publication