arXiv subjects

A. Bazrafshan

Publications and source records attributed to A. Bazrafshan.

16 recordsLinked to original sources

arXiv2026

Quintic Modification to Lifshitz Quasi-topological Black Holes

We extend the analysis of Lifshitz black holes to quintic order in five-dimensional quasi-topological gravity coupled to a massive Abelian vector field. Starting from a static ansatz with a constant-curvature horizon, we derive the reduced field equations and identify the radially conserved quantity of the one-dimensional effective system. We then analyze the algebraic conditions that permit Lifshitz backgrounds, both in the absence and in the presence of the massive vector field. Since closed-form black-hole solutions are not available for the generic quintic theory, we construct numerical solutions using near-horizon expansions and a shooting method. We present solutions for the relativistic branch $z=1$ and the Lifshitz branch $z=2$, covering the three horizon topologies $k=-1,0,+1$. The numerical profiles of the metric functions and the gauge-field function show behavior that is qualitatively consistent with earlier studies of cubic and quartic quasi-topological Lifshitz black holes. We also compute the Wald entropy and Hawking temperature, and examine the local thermal behavior through logarithmic entropy -- temperature plots. For the representative parameter choices considered here, the numerical branches shown possess positive heat capacity.

gr-qc↗

arXiv2025

Thermodynamics and Multi-Horizon Solutions in Quartic Quasitopological Gravity: A Power-Maxwell Approach

In this paper, we derive exact black hole solutions within the framework of fourth-order quasitopological gravity (4QTG) coupled to power-law Maxwell electrodynamics in five-dimensional spacetimes. We explore the thermodynamic properties of these solutions, including entropy, temperature, and electric potential, and verify the validity of the first law of thermodynamics. Our analysis spans asymptotically anti-de Sitter (AdS), de Sitter (dS), and flat spacetimes, revealing that thermal stability is exclusively achievable in asymptotically AdS black holes, while dS and flat solutions exhibit universal instability. The study highlights the unique role of higher-curvature terms in modifying black hole thermodynamics and horizon structures, providing new insights into the interplay between geometry, thermodynamics, and quantum gravity via the AdS/CFT correspondence. Furthermore, we demonstrate that 4QTG supports multi-horizon black holes even in the absence of charge, a feature absent in Einstein gravity. These findings underscore the importance of higher-curvature corrections in resolving classical limitations of general relativity and offer new avenues for exploring quantum gravity and holographic duality.

gr-qc↗

arXiv2024

Quasitopological Lifshitz dilaton black brane

We construct a new class of $(n+1)$-dimensional Lifshitz dilaton black brane solutions in the presence of the cubic quasitopological gravity for a flat boundary. The related action supports asymptotically Lifshitz solutions by applying some conditions which are used throughout the paper. We have to add a new boundary term and some new counterterms to the bulk action to have finite solutions. Then we define a finite stress tensor complex by which we can calculate the energy density of the quasitopological Lifshitz dilaton black brane. It is not possible to obtain analytical solutions, and so we use some expantions to probe the functions behaviors near the horizon and at the infinity. Combining the equations, we can attain a total constant along the coordinate $r$. At the horizon, this constant is proportional to the product of the temperature and the entropy and at the infinity, the total constant shows the energ density of the quasitopological Lifshitz dilaton black brane. Therefore, we can reach to a relation between the conserved quantities temperature, entropy and the energy density and get a smarr-type formula. Using the first law of thermodynamics, we can find a relation between the entropy and the temperature and then ontain the heat capacity. Our results show that the quasitopological Lifshitz dilaton black brane solutions are thermally stable for each positive values of the dynamical critiacl exponent, $z$.

hep-th↗

arXiv2024

Thermodynamics of Rotating Lifshitz Dilaton Black Brane in Quartic Quasitopological gravity

In this paper, we obtain the rotating Lifshitz dilaton black brane solutions in the presence of the quartic quasitopological gravity and then probe the related thermodynamics. At first, we obtain the field equations form which a total constant along the radial coordinate $r$ is deduced. Since we cannot solve the solutions exactly, so we investigate their asymptotic behaviors at the horizon and at the infinity. We attain the conserved and thermodynamic quantities such as temperature, angular velocity, entropy, the energy and the angular momentum densities of the rotating quartic quasitopological Lifshitz dilaton black brane. By evaluating the total constant at the horizon and the infinity, we can make a relation between the thermodynamic quantities and so get to a Smarr-type formula. We demonstrate that the thermodynamic quantities of this rotating black brane obey the first law of the thermodynamics. We also study the thermal stability of the rotating quartic quasitopological Lifshitz dilaton black brane and it is not thermally stable.

hep-ph↗

arXiv2023

Reissner-Nordström Black Holes in Quintic Quasi-topological Gravity

This paper investigates charged black holes within the framework of quintic quasi-topological gravity, focusing on their thermodynamics, conserved quantities, and stability. We construct numerical solutions and explore their thermodynamic properties, supplemented by the study of analytically solvable special cases. By verifying the first law of thermodynamics, we validate our approach and compare our findings to those of Einstein gravity. The physical properties of the solutions are examined across anti-de Sitter, de Sitter, and flat spacetime backgrounds. Our analysis reveals that anti-de Sitter solutions demonstrate thermal stability, while de Sitter and flat solutions lack this property. Finally, we discuss the implications of our results and propose potential avenues for future research in this field.

gr-qc↗

arXiv2021

Surface Terms of Quintic Quasitopological Gravity and Thermodynamics of Quasi-Topological Magnetic Brane Coupled to Nonlinear Electrodynamics

For the the quintic quasitopological action which has no well-defined variational principle, we introduced a surface term that for a spacetime with flat boundaries make the action well-defined. Moreover, we investigated the numerical solutions of the above-mentioned gravity coupled to the nonlinear logarithmic and exponential electrodynamics. It has no horizon and curvature except one conical singularity at $r=0$ with a deficit angle $δϕ$. Also we found the counterterm which removes non-logarithmic divergences for the static quintic quasitopological gravity. Using this counterterm one can calculate a finite action and conserved quantities for the quintic quasitopological gravity.

gr-qc↗

arXiv2019

Thermodynamics of static solutions in (n+1)-dimensional Quintic Quasitopological gravity

Based on the fact that some important theories like string and M-theories predict spacetime with higher dimensions, so, in this paper, we aim to construct a theory of quintic quasitopological gravity in higher dimensions ($n\geq5$). This $(n+1)$-dimensional quintic quasitopological gravity can also lead to the most second-order linearized field equations in the spherically symmetric spacetimes. These equations can not be solved exactly and so, we obtain a new class of $(n+1)$-dimensional static solutions with numeric methods. For large values of mass parameter $m$, these solutions yield to black holes with two horizons in AdS and flat spacetimes. For dS solutions, there are two values, $m_{\rm ext}$ and $m_{\rm cri}$, which yield to a black hole with three horizons for $m_{\rm ext}<m<m_{\rm cri}$. We also calculate thermodynamic quantities for this black hole such as entropy and temperature and check the first law of thermodynamics. Finally, we analyze thermal stability of the $(n+1)$-dimensional static black hole at the horizon $r_{+}$. Unlike dS solutions, AdS ones have thermal stability for each values of $k$, but flat solutions are stable with just $k=1$.

hep-th↗

arXiv2019

Physical and thermodynamic properties of quartic quasitopological black holes and rotating black branes with nonlinear source

In this paper, we find the solutions of quartic quasitopological black holes and branes coupled to logarithmic and exponential forms of nonlinear electrodynamics. These solutions have an essential singularity at $r=0$. Depending on the value of charge parameter $q$, we have an extreme black hole/brane, a black hole/brane with two horizons or a naked singularity. For small values of parameter $q$, the solutions lead to a black hole/brane with two horizons. The values of the horizons are independent of the values of quasitopological parameters and depend only on the values of $q$, dimensions $n$, nonlinear parameter $β$ and mass parameter. Also, the solutions are not thermally stable for dS and flat spacetimes. However, AdS solutions are stable for $r_{+}>{r_{+}}_{\rm{ext}}$ which the temperature is zero for $r_{+}={r_{+}}_{\rm{ext}}$. The value of ${r_{+}}_{\rm{ext}}$ also depends on the values of parameters $q$, $β$, $n$ and $m$. As the value of ${r_{+}}_{\rm{ext}}$ decreases, the region of stability becomes larger. We also use HPEM metric to probe GTD formalism for our solutions. This metric is successful to predict the divergences of the scalar curvature exactly at the phase transition points. For large values of parameter $Ξ$, the black hole/brane has a transition to a stable state and stays stable.

gr-qc↗

arXiv2019

Quasi-Topological Magnetic Brane coupled to Nonlinear Electrodynamics

In this paper, we are eager to construct a new class of (n+1)-dimensional static magnetic brane solutions in quasi-topological gravity coupled to nonlinear electrodynamics such as exponential and logarithmic forms. The solutions of this magnetic brane are horizonless and have no curvature. For ρnear r_{+}, the solution f(ρ) is dependent to the values of parameters q and n and for larger ρ, it depends on the coefficients of Love-Lock and quasi-topological gravities λ, μand c. The obtained solutions also have a conic singularity at r=0 with a deficit angle that is only dependent to the parameters q, n and β. We should remind that the two forms of nonlinear electrodynamics theory have similar behaviors on the obtained solutions. At last, by using the counterterm method, we obtain conserved quantities such as mass and electric charge. The value of the electric charge for this static magnetic brane is obtained zero.

physics.gen-ph↗

arXiv2018

Third order quasi-topological black hole with power-law Maxwell nonlinear source

In this paper, we construct a new class of solutions for five dimensional third order quasi-topological black holes coupled to a power-law Maxwell nonlinear electrodynamics. To have real solutions, we should establish condition $μ<-\frac{λ^2}{3}$ and to have finite solutions at infinity, the parameter of power-law Maxwell theory "s" should obey $\frac{1}{2}<s\leq 2$. Power-law Maxwell lagrangian is successful to set conformal invariance in higher dimensions. Also, this theory can reduce the divergence of the electrical field at the origin that is caused in linear Maxwell theory. As the value of parameter "s" increases, this divergence reduces more. In asymptotically anti-de sitter spacetimes, these obtained solutions lead to a black hole with two horizons for small values of $s$ and $q$. Also, solutions for $s=2$ have different behaviors with respect to the ones for other values of $s$. For negative and small values of parameter $μ$, these solutions can describe a black hole with two horizons. An other important tip is that this black hole has thermal stability just for anti-de sitter solutions if its temperature is positive.

gr-qc↗

arXiv2018

Reissner-Nordstrom Black Holes in Quartic Quasi-Topological Gravity Theory

In this paper, we construct the exact solutions of Reissner-Nordstrom black holes in the presence of quartic quasi-topological gravity. we obtain the thermodynamics and conserved quantities of the solutions and check the first law of thermodynamics. In studying the physical properties of the solutions, we consider asymptotically Ads, dS and flat solutions of Reissner-Nordstrom black hole in quartic quasi-topological gravity and compare them with Einstein and third-order quasi-topological gravities. we also investigate the thermal stability of the solutions that we show the thermal stability are just for AdS solutions not for dS and flat ones.

gr-qc↗

arXiv2017

Magnetic Brane of Cubic Quasi-Topological Gravity in the Presence of Maxwell and Born-Infeld Electromagnetic Field

The main purpose of the present paper is analyzing magnetic brane solutions of cubic quasi-topological gravity in the presence of a linear electromagnetic Maxwell field and a nonlinear electromagnetic Born-Infeld field. We show that the mentioned magnetic solutions have no curvature singularity and also no horizons, but we observe that there is a conic geometry with a related deficit angle. We obtain the metric function and deficit angle and consider their behavior. We show that the attributes of our solution are dependent on cubic quasi-topological coefficient and the Gauss-Bonnet parameter.

hep-th↗

arXiv2012

Surface Terms of Quartic Quasitopological Gravity and Thermodynamics of Nonlinear Charged Rotating Black Branes

As in the case of Einstein or Lovelock gravity, the action of quartic quasitopological gravity has not a well-defined variational principle. In this paper, we first introduce a surface term that makes the variation of quartic quasitopological gravity well defined. Second, we present the static charged solutions of quartic quasitopological gravity in the presence of a non linear electromagnetic field. One of the branch of these solutions presents a black brane with one or two horizons or a naked singularity depending on the charge and mass of the solution. The thermodynamic of these black branes are investigated through the use of the Gibbs free energy. In order to do this, we calculate the finite action by use of the counterterm method inspired by AdS/CFT correspondence. Introducing a Smarr-type formula, we also show that the conserved and thermodynamics quantities of these solutions satisfy the first law of thermodynamics. Finally, we present the charged rotating black branes in $(n+1)$ dimensions with $k\leq [n/2]$ rotation parameters and investigate their thermodynamics.

hep-th↗

arXiv2012

Black Holes in (Quartic) Quasitopological Gravity

We construct quartic quasitopological gravity, a theory of gravity containing terms quartic in the curvature that yields second order differential equations in the spherically symmetric case. Up to a term proportional to the quartic term in Lovelock gravity we find a unique solution for this quartic case, valid in any dimensionality larger than 4 except 8. This case is the highest degree of curvature coupling for which explicit black hole solutions can be constructed, and we obtain and analyze the various black hole solutions that emerge from the field equations in $(n+1)$ dimensions. We discuss the thermodynamics of these black holes and compute their entropy as a function of the horizon radius. We then make some general remarks about $K$-th order quasitopological gravity, and point out that the basic structure of the solutions will be the same in any dimensionality for general $K$ apart from particular cases.

hep-th↗

arXiv2011

Asymptotically AdS Magnetic Branes in (n+1)-dimensional Dilaton Gravity

We present a new class of asymptotically AdS magnetic solutions in ($n+1$)-dimensional dilaton gravity in the presence of an appropriate combination of three Liouville-type potentials. This class of solutions is asymptotically AdS in six and higher dimensions and yields a spacetime with longitudinal magnetic field generated by a static brane. These solutions have no curvature singularity and no horizons but have a conic geometry with a deficit angle. We find that the brane tension depends on the dilaton field and approaches a constant as the coupling constant of dilaton field goes to infinity. We generalize this class of solutions to the case of spinning magnetic solutions and find that, when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters. Finally, we use the counterterm method inspired by AdS/CFT correspondence and compute the conserved quantities of these spacetimes. We found that the conserved quantities do not depend on the dilaton field, which is evident from the fact that the dilaton field vanishes on the boundary at infinity.

hep-th↗

arXiv2010

Topological Black Holes of Einstein-Yang-Mills dilaton Gravity

We present the topological solutions of Einstein-dilaton gravity in the presence of a non-Abelian Yang-Mills field. In 4 dimensions, we consider the $So(3)$ and $So(2,1)$ semisimple group as the Yang-Mills gauge group, and introduce the black hole solutions with spherical and hyperbolic horizons, respectively. The solution in the absence of dilaton potential is asymptotically flat and exists only with spherical horizon. Contrary to the non-extreme Reissner-Nordstrom black hole, which has two horizons with a timelike and avoidable singularity, here the solution may present a black hole with a null and unavoidable singularity with only one horizon. In the presence of dilaton potential, the asymptotic behavior of the solutions is neither flat nor anti-de Sitter. These solutions contain a null and avoidable singularity, and may present a black hole with two horizons, an extreme black hole or a naked singularity. We also calculate the mass of the solutions through the use of a modified version of Brown and York formalism, and consider the first law of thermodynamics.

gr-qc↗