arXiv subjects

J. Sadeghi

Publications and source records attributed to J. Sadeghi.

At least 91 records · Page 5Linked to original sources

arXiv2013

Holograghic Brownian motion in $2+1$ dimensional hairy black holes

In this paper, we investigate the dynamics of a heavy quark under the plasmas correspond to three dimensional hairy black holes. We utilize the AdS/CFT correspondence to study the holographic Brownian motion of this particle in different kinds of hairy black holes. For uncharged black hole at low frequency limit we derive analytic expressions for correlation functions and response functions and verify that the fluctuation-dissipation theorem holds in the presence of a scalar field in the metric background. In the case of charged black hole, we think that the results are similar to what derived for uncharged black hole.

hep-th↗

arXiv2013

Thermodynamics of string black hole with hyperscaling violation

In this paper, we start with black brane and construct specific space-time which violates hyperscaling. In order to obtain the string solution we apply Null-Melvin-Twist and $KK$-reduction. By using the difference action method we study thermodynamics of system to obtain Hawking-Page phase transition. In order to have hyperscaling violation we need to consider $θ=\frac{d}{2}.$ In that case the free energy $F$ is always negative and our solution is thermal radiation without a black hole. Therefore we find that there is not any Hawking-Page transition. Also, we discuss the stability of system and all thermodynamical quantities.

hep-th↗

arXiv2013

Rotating charged hairy black hole in (2+1) dimensions and particle acceleration

In this paper we construct rotating charged hairy black hole in (2+1) dimensions for infinitesimal black hole charge and rotation parameters. Then we consider this black hole as particle accelerator and calculate the center-of-mass energy of two colliding test particles near the rotating charged hairy black hole in (2+1) dimensions. As we expected, the center-of-mass energy has infinite value.

hep-th↗

arXiv2013

Strong Gravitational Lensing in a Charged Squashed Kaluza- Klein Gödel Black hole

In this paper we investigate the strong gravitational lansing in a charged squashed Kaluza-Klein Gödel black hole. The deflection angle is considered by the logarithmic term proposed by Bozza et al. Then we study the variation of deflection angle and its parameters $\bar{a}$ and $\bar{b}$ . We suppose that the supermassive black hole in the galaxy center can be considered by a charged squashed Kaluza-Klein black hole in a Gödel background and by relation between lensing parameters and observables, we estimate the observables for different values of charge, extra dimension and Gödel parameters.

gr-qc↗

arXiv2013

$AdS_{5}$ black hole at N=2 supergravity

In this paper, we consider the charged non-extremal black hole at five dimensional N = 2 supergravity. We study thermodynamics of AdS_{5} black hole with three equal charges (q_{1} = q_{2} = q_{3} = q). We obtain Schrodinger like equation and discuss the effective potential. Then, we consider the case of the perturbed dilaton field background and find presence of odd coefficients of the wave function. Also we find that the higher derivative corrections have no effect on the first and second even coefficients of the wave function.

hep-th↗

arXiv2013

Binding energy of a holographic deuteron and tritium in anti-de-Sitter space/conformal field theory (AdS/CFT)

In the large 't Hooft coupling limit, the hadronic size of baryon is small and nucleon-nucleon potential is obtained from massless pseudo-scalar exchanges and an infinite tower of spin one mesons exchanges. In this paper we use the holographic nucleon-nucleon interaction and obtain the corresponding potential and binding energy for deuteron and tritium nuclei. The obtained potentials are repulsive at short distances and clearly become zero by increasing distance as we expected.

hep-th↗

arXiv2013

Nucleon-Meson Couplings in One Boson Exchange Potential using Non-Critical String Theory

A non-critical holographic QCD model constructed in the six dimensional Anti-de-Sitter ($AdS_6$) supergravity background is employed to study a the baryon. It is shown that the size of the baryon is of order one with respect to the $λ$, however, it is smaller than the scale of the dual QCD. An effective four dimensional action for the nucleon is obtained in terms of the meson exchange potentials. All meson-nucleon couplings in the non-critical $AdS_6$ background are calculated. Results obtained using our model are compared with predictions of four modern phenomenological interaction models. Also, our numerical results are compared with the results of the Sakai-Sugimoto (SS) model which indicate that the non-critical holographic QCD model can be a good toy to calculate the meson-nucleon couplings.

hep-th↗

arXiv2013

Holograghic Brownian motion in three dimensional Gödel black hole

By using the AdS/CFT correspondence and Gödel black hole background, we study the dynamics of heavy quark under a rotating plasma. In that case we follow Atmaja (JHEP 1304, 021, (2013)) about Brownian motion in BTZ black hole. In this paper we receive some new results for the case of $α^{2}l^{2}\neq1$. This case, we must redefine the angular velocity of string fluctuation. We obtain the time evolution of displacement square that angular velocity and show that it behaves as a Brownian particle in non-relativistic limit. In this plasma, it seems that relating the Brownian motion with physical observables is rather a difficult work. But our results match with Atmaja work in the limit $α^{2}l^{2}\rightarrow1$.

hep-th↗

arXiv2013

Jet Quenching Parameter with Hyperscaling Violation

In this paper we study the behavior of jet quenching parameter in the background metric with hyperscaling violation at finite temperature.The background metric is covariant under a generalized Lifshitz scaling symmetry with the dynamical exponent z and hyperscaling exponent $θ$. We evaluate the jet quenching parameter for certain range of these parameters consistent with the Gubser bound conditions in terms of T, z and $θ$. We compare our results with those from conformal case and experimental data. Then we add a constant electric field to this background and find its effect on the jet quenching parameter.

hep-th↗

arXiv2013

Stability of viscous fluid in Bianchi type-VI model with cosmological constant

In this paper, we investigate Bianchi type-$VI$ cosmological model for the universe filled with dark energy and viscous fluid in the presence of cosmological constant. Also, we show accelerating expansion of the universe by drawing volume scale, pressure and energy density versus cosmic time. In order to solve the Einstein field equations, we assume the expansion scalar is proportional to a component of the shear tensor. Therefore, we obtain the directional scale factors and show the EOS parameter crosses over phantom divided-line.

gr-qc↗

arXiv2013

Phenomenological Fluids from Interacting Tachyonic Scalar Fields

In this paper we are interested to consider mathematical ways to obtain different phenomenological fluids from two-component Tachyonic scalar fields. We consider interaction between components and investigate problem numerically. Statefinder diagnostics and validity of the generalized second law of thermodynamics performed and checked. We suppose that our Universe bounded by Hubble horizon.

gr-qc↗

arXiv2013

Interacting Ghost Dark Energy Models with Variable $G$ and $Λ$

In this paper we consider several phenomenological models of variable $Λ$. Model of a flat Universe with variable $Λ$ and $G$ is accepted. It is well known, that varying $G$ and $Λ$ gives rise to modified field equations and modified conservation laws, which gives rise to many different manipulations and assumptions in literature. We will consider two component fluid, which parameters will enter to $Λ$. Interaction between fluids with energy densities $ρ_{1}$ and $ρ_{2}$ assumed as $Q=3Hb(ρ_{1}+ρ_{2})$. We have numerical analyze of important cosmological parameters like EoS parameter of the composed fluid and deceleration parameter $q$ of the model.

gr-qc↗

arXiv2013

Phenomenological Varying Modified Chaplygin Gas with Variable $G$ and $Λ$: Toy Models for Our Universe

This article motivated by the recent articles and results of two authors. Recently, J. Sadeghi and H. Farahani presented a work [1], where they include viscosity and analyze general model, by this way they extended models considered by M. Khurshudyan [2] and [3]. In this article, We tempt to consider varying Modified Chaplygin gas model in case of variable $G$ and $Λ$. It is well known, that varying $G$ and $Λ$ gives rise to modified field equations and modified conservation laws. We will consider two different toy models. First model is a Universe with one component phenomenological gas of our consideration, while for the second model we assume existence of a composed fluid of gas and a matter with $P=ω(t)ρ_{m}$. Sign changeable interaction between fluids is accepted. We will analyze important cosmological parameters like EoS parameter of a fluid, deceleration parameter $q$ of the model.

gr-qc↗

arXiv2013

Thermodynamics of a charged hairy black hole in (2+1) dimensions

In this paper we study thermodynamics, statistics and spectroscopic aspects of a charged black hole with a scalar hair coupled to the gravity in (2+1) dimensions. We obtained effects of the black hole charge and scalar field on the thermodynamical and statistical quantities. We find that scalar charge may increase entropy, temperature and probability, while may decrease black hole mass, free and internal energy. Also electric charge increases probability and decreases temperature and internal energy. Also we investigate stability of the system and find that the thermodynamical stability exists.

hep-th↗

arXiv2013

Interacting Entropy-Corrected Holographic Dark Energy and IR Cut-Off Length

In this paper we consider holographic dark energy model with corrected holographic energy density and show that this model may be equivalent to the modified Chaplygin gas model. Then we obtain relation between entropy corrected holographic dark energy model and scalar field models. We do these works by using choices of IR cut-off length proportional to the Hubble radius, the event horizon radius, the Ricci length, and the Granda-Oliveros length.

gr-qc↗

arXiv2012

Thermodynamics of Schrödinger black holes with hyperscaling violation

In this work, we follow Kim and Yamada (JHEP1107 (2011) 120) and utilize AdS in light-cone frame to derive thermodynamic and transport properties of two kinds of Schrödinger black holes with hyperscaling violation. In that case, we show entropy and temperature are depend on $θ$. In $θ=0$ we see our results are agree with the work of Kim and Yamada. We also construct R-charged black hole with hyperscaling violation and obtain thermodynamics and transport properties.

hep-th↗

arXiv2012

Energy loss and jet quenching parameter in a thermal non-relativistic, non-commutative Yang-Mills plasma

In this paper we consider the problem of a moving heavy quark through a hot non-relativistic, non-commutative Yang-Mills plasma. We discuss about the configuration of the static quark and obtain the quasi-normal modes. Also we find the diffusion constant for the moving heavy quark. The main goal of this study is calculating the jet-quenching parameter for the non-relativistic, non-commutative theory and comparing it with drag forces which recently obtained from the another independent work [1]

hep-th↗

arXiv2012

Strong Gravitational Lensing in a Charged Squashed Kaluza- Klein Black hole

In this paper we investigate the strong gravitational lensing in a charged squashed Kaluza-Klein black hole. We suppose that the supermassive black hole in the galaxy center can be considered by a charged squashed Kaluza-Klein black hole and then we study the strong gravitational lensing theory and estimate the numerical values for parameters and observables of it. We explore the effects of the scale of extra dimension $ρ_0$ and the charge of black hole $ρ_q$ on these parameters and observables.

gr-qc↗