arXiv subjects

Jafar Sadeghi

Publications and source records attributed to Jafar Sadeghi.

At least 55 records · Page 3Linked to original sources

arXiv2023

G-constant-roll inflation

The constant-roll inflation in the context of Galilean inflation or G-inflation is analyzed. By considering a coupling function $G(φ,χ)\propto g(φ)\,χ^n$ for the model of G-inflation, we find different expressions for a suitable development of a model inflationary in the context of constant roll inflation. In order to obtain analytical solutions, we analyze two specific cases; $g(φ)=φ$ and $n=0$, i.e., $G(φ,χ)\propto\,φ$ and when $g(φ)=$ constant and $n=1$ with which $G(φ,χ)\propto\,χ$. In both cases, we find different expressions for the reconstruction of the background variables and the cosmological perturbations in the framework the constant roll inflation. We utilize recent astronomical observations to constrain the different parameters appearing in the stage of constant roll condition as well in the coupling function $G(φ,χ)$.

gr-qc↗

arXiv2023

WGC and WCCC of black holes with quintessence and cloud strings in RPS space

In this paper, we first introduce the Riesner-Nordstrom AdS (RN-AdS) black hole in presence of quintessence and cloud of strings. And then we use the Restrict Phase Space $(RPS)$ formalism in the corresponding black holes at the critical point with equation state $ω_q =-\frac{1}{3},-\frac{2}{3},-1 $. We take advantage from the central charge and Newton's constant with form of variable and prove the compatibility between weak gravity conjecture (WGC) and weak cosmic censorship conjecture (WCCC). Here, we show that when we use the usual RN-AdS black hole with $\frac{Q}{M}>\sqrt{G}$ condition, we have weak gravity conjecture. But, in that case, the WCCC is violated by WGC conjecture. In order to avoid such violation, we consider the Riesner-Nordstrom AdS (RN-AdS) black hole in the presence of quintessence, quintessence, and cloud strings. Here, also one can say that, by using the special central charge, chemical potential, appropriate quintessence, cloud strings parameters, and the effective Newton's constant with suitable conditions one can arrive the compatibility between weak gravity conjecture and weak cosmic censorship conjecture.

hep-th↗

arXiv2023

Strong Cosmic Censorship in light of Weak Gravity Conjecture for Charged Black Holes

In this paper, we investigate the strong cosmic censorship conjecture (SCC) for charged black holes in the de Sitter space by considering the weak gravity conjecture (WGC). Using analytical methods, we find that the SCC is preserved for dS-charged black holes with respect to some restriction $qQ\gg1$ and $r_+\geq Q$ with the help of the WGC condition viz $\frac{q}{m}\geq 1$ for scalar fields. Where q, m are the charge and mass of the scalar field, and $r_+$, Q determine the radius of the outer event horizon and the charge of the black hole, respectively. In that case, when the (WGC) is valid, SCC will definitely be satisfied for the dS-charged black holes. On the other hand, the SCC is violated when the WGC is not satisfied. Also, we examined the RN-dS charged black hole in the extremality state and found that SCC can be violated with the condition $Λr_+^2=1$.

hep-th↗

arXiv2022

Scalar Weak Gravity Conjecture in Super Yang-Mills Inflationary Model

In this article, we want to check four inflation models, such as composite NJL inflation (NJLI), Glueball inflation(GI), super Yang-Mills inflation (SYMI), and Orientifold inflation (OI), with two conjectures of the swampland program: scalar weak gravity conjecture (SWGC) and strong scalar weak gravity conjecture (SSWGC) since all these models violate the dS swampland conjecture(DSC) but are compatible with further refining de Sitter swampland conjecture (FRDSSC) through manual adjustment of free parameters of the mentioned conjecture. We want to study the simultaneous compatibility of each model with these two new conjectures. Despite being consistent with (FRDSSC), we find that all models are not compatible with the other conjectures of the Swampland program in all regions, and these conjectures are only satisfied in a specific area. Also, due to the presence of constant parameter $(ϕ_{0})$ in the higher orders derivatives, the (SYMI) and (OI) among all the models are more compatible with all conjectures of the swampland program. These models can provide a more significant amount of satisfaction with all of them. They can be suitable and accurate inflation models for a more profound examination of universe developments. We determined a particular region for these models is compatible with (FRDSSC), (SWGC), and (SSWGC) simultaneously

astro-ph.CO↗

arXiv2022

RPS Thermodynamics of Taub-NUT AdS Black Holes in the Presence of Central Charge and the Weak Gravity Conjecture

We study the thermodynamics of the Taub-NUT AdS black holes by Visser holographic method using AdS radius as a constant parameter under the restricted phase space approach. Instead of the variables $P$ and $V$, we deal with the central charge and also chemical potential as a unique couple of conjugate thermodynamic variables. We study some interesting properties of the Taub-NUT black holes e.g. supercritical phase equilibrium in the $T-S$ processes, $Q-Φ$ and the Hawking-Page phase transition in the $μ-C$ processes. As a consequence, the consistency of the weak gravity conjecture of multi-charge for Taub-NUT-AdS black holes at critical points is proved. We conclude that in the presence of the central charge and assuming $C=\frac{3}{8}\ell^2$, weak gravity conjecture could be satisfied in the Taub-NUT-AdS black holes with $\hat{n}\ll 1$.

hep-th↗

arXiv2022

Weak Gravity Conjecture from Conformal Field Theory: A Challenge from Hyperscaling Violating and Kerr-Newman-AdS Black Holes

We search for a possible relation between weak gravity conjecture and conformal field theory in the hyperscaling violating and Kerr-Newman-AdS black holes. We deal with the critical points of the black hole systems through the correlation function introduced in conformal field theory. We discuss the weak gravity conjecture conditions by the imaginary part of the energy obtained from the critical points and their poles. Under the assumptions $z=1$, $d=1$ and $θ\rightarrow0^{-}$, we link weak gravity conjecture to the hyperscaling violating black holes due to the existence of $r_{H}$ larger and smaller than one. As the second black hole system, we study the conditions of weak gravity conjecture for the Kerr-Newman-AdS black hole by rotation and radius parameters. Then, we show that the conditions of weak gravity conjecture are satisfied when the charged particle near the hyperscaling violating and Kerr-Newman black holes is $\frac{1}{a}$ with a ratio $\frac{a}{\ell}\ll 1$.

hep-th↗

arXiv2022

Weak Gravity Conjecture of Charged-Rotating-AdS Black Hole Surrounded by Quintessence and String Cloud

A series of corrections to general relativity have recently been applied to find the relationship between entropy and extremality-bound black holes. This relationship has been investigated for many black holes, such as charged AdS, rotating, and massive gravity black holes. We give a minor constant correction to the action and confirm these universal relations for a charged-rotating-AdS black hole. We then examine these calculations for the black hole, surrounded by the quintessence and the cloud of string. In this paper, we evaluate a new universal relation. It means that we find the relation between the extremal mass of the black hole and the factor of cloud string and observe that the corresponding universal relation is well established. We find that the quintessence terms play a very effective role in calculating the mass-charge ratio and concept of weak gravity conjecture of black holes. We note here that the added constant correction is inversely related to the entropy of the black hole. It leads us to see that the mass-to-charge ratio decreases and fully confirms the black hole's weak gravity conjecture (WGC).

gr-qc↗

arXiv2022

Anisotropic constant-roll inflationary scenario with complex quintessence field and swampland conjectures

In this paper, with the presence of swampland conjecture, we use the complex form of a scalar field and investigate the anisotropic constant-roll of an inflationary scenario. Recently, the complex quintessence field has been used to describe the accelerating expansion of the universe which has had interesting results connecting with various conditions. Therefore, the Lagrangian density of the quintessence field leads to obtaining the equations of the complex scalar field. Also, we use the anisotropic constant-roll conditions and the field equation and calculate the exact solutions for some cosmology parameters such as Hubble parameter and potential. Using the exact solution of potential and refined swampland conditions, we plot some figures. In that case, the figures lead us to have challenges between three concepts as complex quintessence, anisotropic constant-roll conditions, and swampland conjectures. Then we discuss their compatibility and incompatibility with corresponding results. Finally, we will analyze the complex quintessence in examining the inflationary scenario.

gr-qc↗

arXiv2022

Warm inflation with bulk viscous pressure for different solutions of an anisotropic universe

We study a warm inflationary model for different expansions assuming an anisotropic universe described by Bianchi I metric. The universe is filled with a scalar field or inflaton, radiation, and bulk viscous pressure. We carry out the inflationary analysis for different solutions of such universe in two different cases of the bulk viscosity coefficient $ξ$ and the dissipation coefficient $Γ$ as constant and variable parameters, respectively. We compare the obtained results with the recent observations, in order to find the observational constraints on the parameters space of the models. Moreover, we attempt to present a better judgment among the considered models by calculation of the non-linear parameter $f_{NL}$ describing the non-Gaussianity property of the models. Additionally, we investigate the warm inflationary models with viscous pressure from the Weak Gravity Conjecture approach, considering the swampland criteria.

gr-qc↗

arXiv2021

Quintessential constant-roll inflation

We investigate a single field model in the context of the constant-roll inflation in which inflaton moves down to the minimum point of the potential with a constant rate of rolling. We use a quintessential inflationary model obtained by a Lorentzian function which is dependent on the number of e-folds. We present the inflationary analysis for the model and find the observational constraints on the parameters space using the observations of CMB anisotropies \textit{i.e.} the Planck and Keck/array datasets. We find the observationally acceptable values of the Width of the Lorentzian function as $0.3<Γ\leq0.5$ at the $68\%$ CL and $Γ\leq0.3$ at the $95\%$ CL when $ξ=120$, $|β|=0.02$ and $N=60$. Also, we acquire the observationally favoured values of the amplitude of the Lorentzian function as $400<ξ\leq600$ at the $68\%$ CL and $ξ\leq400$ at the $95\%$ CL when $Γ=0.1$, $|β|=0.02$ and $N=60$. Moreover, we study the model from the Weak Gravity Conjecture approach using the swampland criteria.

astro-ph.CO↗

arXiv2021

Constant-roll $f(R)$ inflation compared with Cosmic Microwave Background anisotropies and swampland criteria

Inflationary models derived from $f(R)$ gravity, where the scalaron rolls down with a constant rate from the top to the minimum of the effective potential, are considered. Specifically, we take into account three $f(R)$ models \textit{i.e.}\,Starobinsky $R^{2}$, $R^{2p}$ and the logarithmic corrected models. We compare the inflationary parameters derived from the models with the observational data of CMB anisotropies \textit{i.e.} the Planck and Keck/array datasets in order to find observational constraints on the parameters space. We find that although our $f(R)$ constant-roll models for $γ=0$ show observationally acceptable values of $r$, they do not predict favoured values of the spectral index. In particular, we have $n_{s}>1$ for the Starobinsky $R^{2}$ and $R^{2p}$ models and $0.996<n_{s}<0.999$ for logarithmic model. Finally, we study the models from the point of view of Weak Gravity Conjecture adopting the swampland criteria.

gr-qc↗

arXiv2021

Nonminimal coupling inflation with constant slow roll

We study a single field inflationary model modified by a non-minimal coupling term between the Ricci scalar $R$ and the scalar field $φ$ in the context of constant-roll inflation. The first-order formalism is used to analyse the constant-roll inflation instead of the standard methods used in the literature. In principle, the formalism considers two functions of the scalar field, $W=W(φ)$ and $Z=Z(φ)$, which lead to the reduction of the equations of motion to first-order differential equations. The approach can be applied to a wide range of cosmological situations since it directly relates the function $W$ with Hubble parameter $H$. We perform the inflationary analysis for power-law and exponential couplings, separately. Then, we investigate the features of constant-roll potentials as inflationary potentials. Finally, we compare the inflationary parameters of the models with the observations of CMB anisotropies in view of realize a physically motivated model.

gr-qc↗

arXiv2021

The generalized $sl(2, R)$ and $su(1, 1)$ in non-minimal constant-roll inflation

In the present work, we consider the non-minimal coupling inflationary model in the context of the constant-roll idea which is investigated by the first-order formalism. We attempt to find the hidden symmetries behind the model by the Lie symmetry method. We supply this aim by using the symmetry features of the Heun function instead of Killing vector approach. We show that the hidden symmetries of the non-minimal constant-roll inflation in the cases of power-law and exponential couplings are characterized as a generalized form of $sl(2, R)$ and $su(1, 1)$ algebra, respectively.

gr-qc↗

arXiv2020

The Schwarzschild/CFT Correspondence: Weyl Rescaled Case

In this work, the CFT dual of the Schwarzschild black hole is investigated. A Weyl rescaling factor is presented, so that the Weyl rescaled Schwarzschild metric, after a coordinate transformation, has an $AdS_{2} \times S^{2}$ geometry at vicinity of its origin. Since the near origin spacetime admits an $AdS_{2}$ factor, it is dealt with a 2D effective gravity which is dimensionally reduced from the near origin solution. It is exhibited that the dual CFT has a central charge $c=96 M^3$ which is an asymptotic conserved charge of the effective solution. Finally, the microscopic entropy of Schwarzschild black hole is achieved by using Cardy formula. It is revealed that the microscopic entropy exactly reproduces the Bekenstein-Hawking entropy of the Schwarzschild black hole.

hep-th↗

arXiv2017

Quantum Tunneling from the Charged Non-Rotating BTZ Black Hole with GUP

In the present paper, the quantum corrections to the temperature, entropy and specific heat capacity of the charged non-rotating BTZ black hole are studied by generalized uncertainty principle in tunneling formalism. It is shown that quantum corrected entropy would be of the form of predicted entropy in quantum gravity theories like string theory and loop quantum gravity.

hep-th↗

arXiv2015

Conformal Transformations, Rotating String and Effects of angular velocity on Accelerating Quark-Antiquark pair in $AdS_3$

In order to study quark and anti-quark interaction, one should consider all effects of the medium in motion of the pair. Because the pair, is not produced at rest in QGP. So the velocity of the pair, has some effects on its interactions that should be taken into account. In this paper we apply some conformal transformations for a rotat- ing string dual to a rotating heavy quark in $AdS_3$ which construct an accelerating string dual to an accelerating quark and anti-quark pair. So, we can have a comparison between when pair has angular velocity or not. Then we can study effects of angular velocity on the accelerating quark and anti-quark which are constructed by performing special con- formal transformations, conformal SO(2,2) transformation and particular $SL(2,R)_L$ and $SL(2,R)_R$ transformation. The accelerating quark and anti-quark show different behavior with increasing in angular velocity. With useful numerical solutions we show that quark and anti-quark can deccelerate to achieve each other or accelerate to get away from each other. We will see variable behaviors of the pair in different transformations. There are various behavior like, permanent behavior, increase or decrese in acceleration or we will consider uncertain behavior.

hep-th↗

arXiv2015

Phase plane analysis and statefinder diagnostic of agegraphic dark energy in 5D Brans-Dicke cosmology

We present an autonomous phase-plane describing the evolution of field equations containing an agegraphic dark energy in 5D Brans- Dicke cosmology. To observationally verify the numerical results, we simultaneously solve the equations by constraining the model parameters with SNe Ia data. We find conditions for the existence and stability of the critical points (states of the universe) and numerically examine the cosmological parameters. We also investigate the model by means of statefinder diagnostic.

gr-qc↗

arXiv2014

Hydrodynamics in black brane with hyperscaling violation metric background

In this paper we consider a metric with hyperscaling violation on black brane background. In this background we calculate the ratio of shear viscosity to entropy density with hydrodynamics information. The calculation of this quantity lead us to constraint $θ$ as $3\leqθ<4$, and $θ\leq0$. In that case we show that the quantity of $\fracη{s}$ not dependent to hyperscaling violation parameter $θ.$ Our results about ratio of shear viscosity to entropy density in direct of $QCD$ point of view agree with other works in literature as $1/4π$.

hep-th↗