arXiv subjects

J. Sadeghi

Publications and source records attributed to J. Sadeghi.

At least 55 records · Page 3Linked to original sources

arXiv2019

The equivalence between Finsler and non-commutative geometries by massive gravity black hole

In the present work, we wanted to find the possible way in order to make the equivalence between non-commutative and Finsler geometries as two useful mathematical tools. Based on this purpose, we were concerned to search this possibility by investigating the massive gravity black holes. Firstly the Lagrangian of the system is introduced and then it is rewritten in the non-commutative regime by definition of the new variables. On the other hand, we focus on the Finsler geometry in order to find a Finslerian function which is equivalent to the mentioned non-commutative Lagrangian under special conditions. Also, the effective potential of the system was calculated as a part of the corresponding conditions.

hep-th↗

arXiv2019

The temperature and entropy corrections on the charged hairy black holes

In this paper, we consider the first order correction of the entropy and temperature in a charged black hole with a scalar field. Here, we apply such correction for the different cases of black holes. These corrections are due to the thermal fluctuations of statistical physics. Also, we take advantage of such corrections and study the $ P - V $ critically and phase transition. Also, we investigate the effect of correction on the critical point and stability of the system. We obtain modified thermodynamics quantities and find effects of thermal fluctuations in the stability of the black hole. We find that stability of black hole is depend on the thermal fluctuations. Finally, we compare the results of the corrected and uncorrected by thermodynamical quantities.

gr-qc↗

arXiv2019

Klein Gordon particle near R-N black hole, generalized sl(2) algebra and harmonic oscillator energy

In this paper, we consider Klein Gordon particle near Reissner-Nordström black hole. The symmetry of such background lead us to compare the corresponding Laplace equation with the generalized Heun functions. Such relation help us achieve the generalized $sl(2)$ algebra and some suitable results for describing the above mentioned symmetry. On the other hand in case of $r\rightarrow r_{+}$ which is near the proximity black hole, we obtain the energy spectrum and wave function. When we compare the equation of $R-N$ background with Laguerre differential equation, we show that the obtained energy spectrum is same as three dimensional harmonic oscillator. So, finally we take advantage of harmonic oscillator energy and make suitable partition function. Such function help us to obtain all thermodynamical properties of black hole. Also, the structure of obtained entropy lead us to have some bit and information theory in the $R-N$ black hole.

gr-qc↗

arXiv2018

Quark anti-quark entropic force and diffusion constant in a Yang-Mills like theory

The entropic force experienced by a moving quarkonia in a plasma, is computed in a hyperscaling violation background by holography approach. In that case, the axis of the moving quarkonia has an arbitrary angle with wind. We use the results for HSV parameters which obtained in our paper [1] as appropriate values satisfying condition $ImV_{Q\bar{Q}}< 0$. We will show that, in this background the entropic force of the meson shows a decreasing behaviour corresponds to increasing dissociation length. Results of this paper are in agreement with our mentioned work. In addition we will find diffusion constant in an exact case and by an exact approach [2] which satisfies the mentioned condition in there.

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arXiv2018

Effects of dark energy on $P-V$ criticality and efficiency of charged Rotational black hole

In this paper, we study $P-V$ criticality of Kerr-Newman $AdS$ black hole with a quintessence field. We calculate critical quantities and show that for the equation state parameter $ω= -\frac{1}{3}$, the obtained universal ratio ($\frac{P_{c}\upsilon_{c}}{T_{c}}$) is quite same as Kerr-Newman $AdS$ black hole without dark energy parameter. We investigate the influence of quintessence field $α$, equation state parameter $ω$ and angular momentum $J$ on the efficiency $η$. We find that $η$ is increased by increasing $J$ and $α$ and decreasing charge $Q$ of black hole. We show when $ω$ increases from $-1$ to $-\frac{1}{3}$ the efficiency decreases. Also we study ratio $\fracη{η_{C}}$ (which $η_{C}$ is the Carnot efficiency) and see that the second law of the thermodynamics is satisfied by special values of $J$ and $α$ and holds for any value of $Q$. We notice that in this case by increasing $ω$ from $-1$ to $-\frac{1}{3}$ the range of $J$ and $α$ increases.

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arXiv2018

Diffusion coefficient and DC conductivity of anisotropic static black hole

In this study we apply two different methods in the context of $AdS/CFT$ correspondence and calculate the diffusion coefficient and $DC$ conductivity of a four-dimensional spatially anisotropic static black hole. First, the \emph{modified} transport coefficients is obtained by stretched horizon method and Fick's law in the context of the membrane paradigm. In order to do such calculation, we use the Maxwell equations with electromagnetic gauge field propagating in two dimensions. Two dimensional propagating gauge field leads to the complex transport coefficients which is proved by present paper. In second step, we explain electro-thermal method and employ an effective vector field and extract retarded Green's function on the classical boundary. Then, $DC$ conductivity and diffusion coefficient are obtained by using Kubo formula. Our calculation can be applied on two well-known examples of anisotropic black holes as the Einstein-Maxwell-dilaton-axion model and AdS-Einstein-Maxwell-dilaton-axion in massive gravity.

hep-th↗

arXiv2017

The Lagrangian of charged test particle in Horava-Lifshitz black hole and deformed phase space

In this paper, we use deformation approach and obtain the corresponding Lagrangian of charged test particle. Also, we show the effect of NC parameters on the Lagrangian of test particle in HL background with charge and without charge. Also, we see in case of $β=θ$ and without charge, the deformed and non-deformed Lagrangian will be same. Also in case of $β=θ$ and with charge will be the same but the charge or field need some scaling. Finally, We show that two theories in case of $β\neqθ$ with charge is completely different. It means that in case of NC geometry in addition to have time components of field we have $r$ and $x_{i}$ components.

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arXiv2017

The relation between non-commutative and Finsler geometry in Horava-Lifshitz black holes

In this paper we employ the Horava-Lifshitz black holes solutions and obtain the corresponding Hamiltonian. It helps us to take new variables and it will be written by harmonic oscillator form. This leads us to apply non-commutative geometry to the new Hamiltonian and obtain the corresponding Lagrangian. And then, we take some information from Finsler geometry and write the Lagrangian of the different kinds of Horava-Lifshitz black holes. We show that the corresponding Lagrangian in non-commutative and Finsler geometry for above mentioned black holes completely coincidence together with some specification of parameters. But in case of rotation, the place of center of mass energy completely different, so the particle goes to inside of black hole rapidly without falling into singularity. So in that case, two Lagrangians cover each other at $0<r<r_h.$

hep-th↗

arXiv2017

Diffusion constant of slowly rotating black three-brane

In this paper, we take the slowly rotating black three-brane background and perturb it by introducing a vector gauge field. We find the components of the gauge field through Maxwell equations and Bianchi identities. Using currents and some ansatz we find Fick's first law at long wavelength regime. An interesting result for this non-trivial supergravity background is that the diffusion constant on the stretched horizon which emerges from Fick's first law is a complex constant. The pure imaginary part of the diffusion constant appears because the black three-brane has angular momentum. By taking the static limit of the corresponding black brane the well known diffusion constant will be recovered. On the other hand, from the point of view of the Fick's second law, we have the dispersion relation $ω=-iDq^{2}$ and we found a damping of hydrodynamical flow in the holographically dual theory. Existence of imaginary term in the diffusion constant introduces an oscillating propagation of the gauge field in the dual field theory.

hep-th↗

arXiv2017

The stress energy tensor of neutral blackfold and dual theory

In this paper we consider charged and neutral blackfold and extract the Brown-York stress energy tensor. Also, we show that the neutral blackfold spacetime is Ricci- flat and the other spacetime is not. This Ricci-flat condition gives us opportunity to calculate the AAdS spacetime. In order to have dual theory one can consider the AAdS in Fefferman- Graham coordinates. This frame gives correct form of stress tensor in the boundary. The corresponding tensor with using this frame will be traceless and conserved. Such stress tensor is same as perfect fluid and it proves the dual renormalized theory exists for the neutral blackfold .

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arXiv2017

The thermal properties of blackfold and calculation of stress energy tensor

In this paper, we determine thermodynamical quantities for one kind of higher dimensional black holes. We take two charged and neutral blackfold which are higher dimension. We investigate the thermodynamical properties of such black hole at near horizon. By expanding those metrics around horizon, considering periodicity condition of imaginary time and applying some thermodynamical constraints, we extract stress energy tensor of blackfolds. We compare the thermodynamical properties of charged and neutral blackfold. We see here that the stress energy tensor of charged blackfold has brane-tension component in addition to thermal properties. Then by knowing that the spacetime of neutral blackfold is Ricci-flat and there is a nice relation between Ricci-flat and AdS spacetimes we determine the AdS form of Ricci-flat. Also we calculate the corresponding temperature which is satisfied by our previous calculation. Finally, we check the phase transition of blackfolds and show that there is not any critical point for them. So, the thermodynamical stability of both blackfolds will be proven, this result agree with literature.

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arXiv2017

The effect of Quintessence on the low and high temperature behavior of entanglement entropy for boundary field theory dual to AdS black holes

The effect of dark energy on the low and high temperature of strip region of the boundary field theory dual to AdS black holes was studied. In this framework, we investigate this behavior for different types of equation state and different regimes of normalization factor (a). We will see that the change of entanglement entropy is growing up with increasing a and |ω|.

hep-th↗

arXiv2017

The Thermodynamic Efficiency in Static and Dynamic Black Holes

We note that, in extended phase space the cosmological constant is a thermodynamic variable. In this paper, this cosmological constant lead us to consider a black hole as a heat engine. So, here we take advantage from holographic heat engine and study two kind of different black holes. We first investigate a static black hole (Dyonic BH) and consider the necessary condition to have high efficiency. Also we continue our investigation for dynamic black hole (rotating charged black hole) and study the effect of rotating parameter on the thermodynamic efficiency of holographic heat engine. We show that the rotating parameter has a more effective role than electric charge in thermodynamic efficiency.

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arXiv2017

Phase Transition of charged Rotational Black Hole and Quintessence

In this paper, we calculate thermodynamical quantity of Kerr-Newman-AdS black hole solution in quintessence matter. Then, we show that how the rotation and cosmological parameters effect to the thermodynamics properties of black hole. Also, we investigate both types of phase transition for different values of $ω$ parameter in extended phase space. We notice that type one of phase transition occurs for $P<0.42$ and $a<0.5$. And also we see that the phase transition point shifts to higher entropy when pressure $P$, rotation parameter $a$ and $α$ increase. Also, we find that by changing parameter $ω$ from -1 to $-\frac{1}{3}$, the critical point shifts to higher entropy. Then we study type two of phase transition and show critical points increase by increasing parameter $α$. Also, we show that the critical point shifts to higher entropy when $α$, $ω$ and rotation parameter $a$ decrease. Finally, we find that by decreasing pressure the first critical point shifts to lower entropy and second critical point shifts to higher entropy.

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arXiv2017

Deformation of the quintom cosmological model and its consequences

In this paper, we investigate the effects of non-commutative phase-space on the quintom cosmological model. In that case, we discuss $Λ_{1}$, $Λ_{2}$ and other cosmological parameters and show that they are associated to deformation parameters $θ$ and $β$. Generally one can say that, the non-commutative parameter plays important role in physics and here also help us to arrange the divergency of cosmological constant. We draw time-dependent scale factor and investigate the effect of non-commutative parameters. Finally, we take advantage from non-commutative phase-space and obtain the deformed Lagrangian for the quintom model. In order to discuss some cosmological phenomena as dark energy and inflation, we employ Neother symmetry.

hep-th↗

arXiv2017

The investigation of quark - antiquark potential in plasma with hyperscaling violation background

In this paper, we investigate imaginary part of the potential for a moving quarkonia in plasma. In order to verify the validity of imaginary part of the potential we employ hyperscaling violation metric background. In QCD system the imaginary part of potential shows the decay behaviour and the corresponding potential should be negative. The corresponding potential always appears in QCD as an exponential function. We find general constraints for Im$V_{Q\bar{Q}}$ at the near horizon limit and apply them for some known cases. Finally, we find the suitable spatial dimension d, z and $θ$ also rapidity $η$ for two interesting cases. Our calculation with AdS/CFT guarantees the dynamical parameter as a $θ$ in hyperscaling violation metric background. We also present the hyperscaling violationg metric in this context very close to YM theory with finite temperature.

hep-th↗

arXiv2017

Logarithmic corrections of charged hairy black hole in (2+1) dimension

We consider a charged black hole with a scalar field that is coupled to gravity in (2 + 1)-dimensions. We compute the logarithmic corrections to the corresponding system using two approaches. In the first method we take advantage of thermodynamic properties. In the second method we use the metric function that is suggested by conformal field theory. Finally, we compare the results of the two approaches.

gr-qc↗

arXiv2017

The phase transition and holographic in modified Horava -Lifshitz black hole

In this paper, we take cosmological constant as a thermodynamical pressure and it's conjugate quantity as a thermodynamical volume. This expression help us to investigate the phase transition and holographic heat engine. So, in order to have Van der Waals fluid behaviour in Horava -Lifshitz (HL) black hole, we modified the solution of such black hole with some cosmology ansatz. Also from holographic heat engine, we obtain Carnot efficiency for the HL black hole. The phase transition of the system lead us to investigate the stability condition for the corresponding black hole. In that case, we show that the stability exist only in special region of black hole.

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