arXiv subjects

Mohammad Ghanaatian

Publications and source records attributed to Mohammad Ghanaatian.

6 recordsLinked to original sources

arXiv2026

Static Magnetic Brane Solutions in Quartic Quasi-Topological Gravity with Power-Law Maxwell Nonlinear Electrodynamics

In this paper, we derive static magnetic brane solutions in quasi-topological gravity, considering the presence of power-law Maxwell nonlinear electrodynamics. The resulting solutions are horizonless and curvature-free. However, there exists a conic singularity with a deficit angle, which depends solely on the parameters $q$, $n$, and $s$ (where $s$ is the nonlinear parameter). In addition, in order to obtain finite solutions at infinity, the parameter $s$ of the power-law Maxwell theory is constrained to the range $1/2 < s \leq 2$. It is also observed that, for $ρ$ approaching $r_+$, the solutions $f(ρ)$ are dependent on the values of parameters $q$ and $n$, and for larger values of $ρ$, the solutions depend on the coefficients of Lovelock and quasi-topological gravities, namely $λ$, $μ$, and $c$. Finally, we employ the counterterm method to compute the conserved quantities of these spacetimes.

gr-qc↗

arXiv2020

Multiparameter estimation, lower bound on quantum Fisher information and non-Markovianity witnesses of noisy two-qubit systems

By using the quantum Fisher information (QFI), we address the process of \textit{single}-parameter estimation in the presence of bosonic as well as fermionic environments and protection of information against the noise. In particular, the quantum interferometric power (IP) of the evolved state of the system is uncovered as an important lower bound for the QFIs of initially encoded parameters. Moreover, we unveil new witnesses of non-Markovianity, that can be used to detect efficiently the memory effects and backflow of information from the environment to the system. On the other hand, we also investigate the \textit{multiparameter} estimation of initial parameters encoded into the quantum state of a two qubit system and obtain analytical formula of the corresponding QFI matrix. In particular, the corresponding quantum Cramer-Rao bounds in both single and multiparameter estimations are analysed. In addition, we illustrate that the quantum \textit{coherence} and \textit{purity} of the evolved state of the probes are two key elements in realizing optimum multiparameter estimation.

quant-ph↗

arXiv2015

Quartic Quasi-Topological-Born-Infeld Gravity

In this paper, quartic quasi-topological black holes in the presence of a nonlinear electromagnetic Born-Infeld field is presented. By using the metric parameters, the charged black hole solutions of quasi-topological Born-Infeld gravity is considered. The thermodynamics of these black holes are investigated and I show that the thermodynamics and conserved quantities verify the first law of thermodynamics. I also introduce the thermodynamics of asymptotically AdS rotating black branes with flat horizon of these class of solutions and I calculate the finite action by use of the counterterm method inspired by AdS/CFT correspondence.

gr-qc↗

arXiv2014

Investigation of Bouncing Universe and Phantom Crossing in Modified Gravity Coupled with Weyl Tensor and its Reconstruction

In this study, FRW cosmology in modified gravity containing arbitrary function $f(R)$ is taken into consideration when our action are coupled with Weyl tensor. It is indicated that the bouncing solution emerges in the model while the equation of state (EoS) parameter crosses the phantom divider. In this research, cosmological usage of the most promising candidates of dark energy in the framework of $f(R)$ theory coupled by Weyl tensor is explored. A $f(R)$ gravity model in the spatially flat FRW universe according to the ordinary version of the holographic dark energy model, which describes accelerated expansion of the universe is reconstructed. The equation of state parameter of the corresponding Weyl gravity models are obtained as well. We conclude that the holographic and Weyl gravity models can behave like phantom or quintessence models, whereas the equation of state parameter of the models can transit from quintessence state to phantom regime as shown recent observations.

physics.gen-ph↗

arXiv2014

Lifshitz Quartic Quasitopological Black Holes

In this paper we shall elucidate some of the effects of the quartic quasitopological term for Lifshitz-symmetric black holes. The field equations of this theory are difficult to solve exactly; here we will use numerical solutions both to verify previous exact solutions for quartic quasitopological AdS black holes as well as to examine new quasitopological Lifshitz-symmetric black hole solutions, in order to determine the effect of the quartic coupling parameter on the black hole's thermodynamic behavior. We shall find that the quartic parameter controls solutions very similarly to the cubic parameter, allowing for the construction of a theory with another free parameter which may find meaning in the phase transition behaviour of a gauge/gravity context.

hep-th↗

arXiv2013

Nonlinear Charged Black Holes in Anti-de Sitter Quasi-Topological Gravity

In this paper, we present the static charged solutions of quartic quasitopological gravity in the presence of a nonlinear electromagnetic field. Two branches of these solutions present black holes with one or two horizons or a naked singularity depending on the charge and mass of the black hole. The entropy of the charged black holes of fourth order quasitopological gravity through the use of Wald formula is computed and the mass, temperature and the charge of these black holes are found as well. We show that black holes with spherical, flat and hyperbolical horizon in quasitopological gravity are stable for any allowed quasitopological parameters.

gr-qc↗