The energy-momentum tensor for a massless conformally coupled scalar field in the region between ... more The energy-momentum tensor for a massless conformally coupled scalar field in the region between two curved boundaries in k = −1 static Robertson-Walker spacetime is investigated. We assume that the scalar field satisfies the Dirichlet boundary condition on the boundaries. k = −1 Robertson-Walker space is conformally related to the Rindler space, as a result we can obtain vacuum expectation values of energy-momentum tensor for conformally invariant field in Robertson-Walker space from the corresponding Rindler counterpart by the conformal transformation.
Rev. D 77 (2008) 106005], we generalize their work to the non-flat case. We consider a universe f... more Rev. D 77 (2008) 106005], we generalize their work to the non-flat case. We consider a universe filled with matter and show that it is possible to obtain both inflation and accelerated expansion at late times by using a single scalar field. Realistic examples are worked out in order to illustrate this fact. Then we extend the problem to the interacting case.
Inflationary models derived from f (R) gravity, where the scalaron rolls down with a constant rat... more 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 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 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 ns > 1 for the Starobinsky R 2 and R 2p models and 0.996 < ns < 0.999 for logarithmic model. Finally, we study the models from the point of view of Weak Gravity Conjecture adopting the swampland criteria.
We investigate a single field model in the context of the constant-roll inflation in which inflat... more 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 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 ≤ 0.5 at the 68% CL and Γ ≤ 0.3 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 ≤ 600 at the 68% CL and ξ ≤ 400 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.
In this paper, we use corrected $f(R)$ gravitational model which is polynomial function with a lo... more In this paper, we use corrected $f(R)$ gravitational model which is polynomial function with a logarithmic term. In that case, we employ the slow-roll condition and obtain the number of cosmological parameter. This help us to verify the swampland conjectures which is guarantee the validation of low - energy quantum field theory. The obtained results shown that the corresponding model is consistent with the swampland conjectures. Also the upper and lower limit of the parameter \textcolor{red}{$n$} are \textcolor{blue}{0.15} and \textcolor{blue}{0.0033}. Finally, by using scalar spectrum index $ n_{s} $ and tensor to scalar ratio $ r $ relations and compared with Planck 2018 empirical data, we obtain the coefficients $\alpha$,$\beta$ and $\gamma$. Also, the corresponding results are creaked by several figures, literature and also plank 2018 data.
arXiv: General Relativity and Quantum Cosmology, 2020
As we know, there is an area around the event horizon of rotating black holes, which is called by... more As we know, there is an area around the event horizon of rotating black holes, which is called by ergosphere. The corresponding rotational energy of black holes is located to this area. Every particle in this region become dragged by a rotating space-time. This makes possible to extract energy from rotating black holes, which is called the Penrose process. By using the center-of-mass energy, the Penrose process has been applied to the Kerr-Newman black hole \cite{20}. But in this paper, we examine the collision of two spinning massive particles near the corresponding black hole with critical and near-critical angular momentum. In that case, we then calculate the energy of the third particle $E_{3}$ in terms of the first two particles $E_{2}$ and $E_{1}$. We also obtain the parameter $\eta_{max}$ which is the ratio of extracted energy to input energy. We mention that here by exerting the weak gravity conjecture (WGC) we have $\eta_{max}\simeq1.5$ . We see here the WGC condition and r...
In this paper, we consider the problem of a moving heavy quark through a hot nonrelativistic, non... more In this paper, we consider the problem of a moving heavy quark through a hot nonrelativistic, non-commutative Yang-Mills plasma. We discuss about the configuration of the static and dynamic quarks, and also obtain the quasi-normal modes. 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].
Motivated by the recent works of Refs. [1, 2] where a model of inflation has been suggested with ... more Motivated by the recent works of Refs. [1, 2] where a model of inflation has been suggested with non-minimally coupled massive vector fields, we generalize their work to the study of the bouncing solution. So we consider a massive vector field, which is non-minimally coupled to gravity. Also we consider non-minimal coupling of vector field to the scalar curvature. Then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy. Finally we simply plot reconstructed physical quantities in flat universe.
In this paper we consider a quintom model of dark energy with a single scalar field T given by a ... more In this paper we consider a quintom model of dark energy with a single scalar field T given by a Lagrangian which inspired by tachyonic Lagrangian in string theory. We consider non-minimal coupling of tachyon field to the scalar curvature, then we obtain the equation of state (EoS), and the condition required for the model parameters when ω crosses over −1.
In this paper we consider a moving quark in the thermal plasma at the N =2 Supergravity theory. B... more In this paper we consider a moving quark in the thermal plasma at the N =2 Supergravity theory. By using the AdS/CFT correspondence we obtain energy loss of the quark. Then we consider the higher derivative corrections in charged AdS-black hole and calculate the drag force of the moving quark in the thermal plasma. Also we find a limit which N =2 Supergravity solutions are correspondening to the N =4 Super Yang-Mills solutions for the heavy quark.
International Journal of Theoretical Physics, 2012
In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivi... more In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivities for the R-charged black hole in STU model. We generalize previous works to the case of a black hole with three different charges. Actually we use diffusion constant to obtain ratio of shear viscosity to entropy. By applying the thermodynamical stability we recover previous results. Also we investigate the effect of higher derivative corrections.
International Journal of Theoretical Physics, 2008
In this paper, we have considered the curved universe which is filled by tachyonic field. We have... more In this paper, we have considered the curved universe which is filled by tachyonic field. We have found the exact solutions for the field, pressure, density, and scale factor and some cosmological parameters. In such universe, we have investigated the role of tachyonic field in different stages of k for the evolution of the universe. Finally we draw the graphs for the scale factor, Hubble's parameter, energy density, pressure, acceleration parameter, equation of state and potential for the different values of k. Also we obtained the exact form of field which shows that the tachyonic field has the kink form.
We study a warm inflationary model for different expansions assuming an anisotropic universe desc... more 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 fNL 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.
In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: ... more In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: see text] model by considering two different statements of shape [Formula: see text] and redshift [Formula: see text] functions. We calculate the parameters of the model including energy density [Formula: see text], tangential pressure [Formula: see text] and radial pressure [Formula: see text] for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots.
In the present work, we consider the non-minimal coupling inflationary model in the context of th... more 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.
In this paper, we impose gravitational perturbations to the static configuration of flat space-ti... more In this paper, we impose gravitational perturbations to the static configuration of flat space-time and study the stability conditions. We also investigate the presence of supersymmetry by using factorization method. In this way, by studying the shape invariance we get to the allowed frequency spectrum and also the supercharges algebra for the first time. We show that the geometric fluctuations cause unstable modes and yield the negative spectra of oscillation.
We investigate a single field model in the context of the constant-roll inflation in which inflat... more 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 Lorentzian function which is dependent on the number of e-folds in order to obtain the slow-roll parameters. We present the inflationary analysis for the model and find the observational constraints on the parameters space using the observations of CMB anisotropies 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 ≤ 0.5 at the 68% CL and Γ ≤ 0.3 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 ≤ 600 at the 68% CL and ξ ≤ 400 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.
The imaginary potential and entropic force are two important different mechanisms to characterize... more The imaginary potential and entropic force are two important different mechanisms to characterize the dissociation of heavy quarkonia. In this paper, we calculate these two quantities in strongly coupled theories with anisotropic Lifshitz scaling and hyperscaling violation exponent using holographic methods. We study how the results are affected by the hyperscaling violation parameter $$ \theta $$ θ and the dynamical exponent z at finite temperature and chemical potential. Also, we investigate the effect of the chemical potential on these quantities. As a result, we find that both mechanisms show the same results: the thermal width and the dissociation length decrease as the dynamical exponent and chemical potential increase or as the hyperscaling violating parameter decreases.
International Journal of Theoretical Physics, 2013
In this paper we consider Gödel black hole and study thermodynamics and statistics with logarithm... more In this paper we consider Gödel black hole and study thermodynamics and statistics with logarithmic correction. We calculate some important quantities such as free energy, specific heat and partition function.
We study the first-order formalism for the two coupled scalar fields with the superpotential W (φ... more We study the first-order formalism for the two coupled scalar fields with the superpotential W (φ, χ). As we know, the cosmological solution crucially depends on the coupled scalar fields. Here, we deform the corresponding superpotential and obtain the solution for some cosmological parameters. Finally, we compare the deformed and non-deformed solutions with the different figures.
The energy-momentum tensor for a massless conformally coupled scalar field in the region between ... more The energy-momentum tensor for a massless conformally coupled scalar field in the region between two curved boundaries in k = −1 static Robertson-Walker spacetime is investigated. We assume that the scalar field satisfies the Dirichlet boundary condition on the boundaries. k = −1 Robertson-Walker space is conformally related to the Rindler space, as a result we can obtain vacuum expectation values of energy-momentum tensor for conformally invariant field in Robertson-Walker space from the corresponding Rindler counterpart by the conformal transformation.
Rev. D 77 (2008) 106005], we generalize their work to the non-flat case. We consider a universe f... more Rev. D 77 (2008) 106005], we generalize their work to the non-flat case. We consider a universe filled with matter and show that it is possible to obtain both inflation and accelerated expansion at late times by using a single scalar field. Realistic examples are worked out in order to illustrate this fact. Then we extend the problem to the interacting case.
Inflationary models derived from f (R) gravity, where the scalaron rolls down with a constant rat... more 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 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 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 ns > 1 for the Starobinsky R 2 and R 2p models and 0.996 < ns < 0.999 for logarithmic model. Finally, we study the models from the point of view of Weak Gravity Conjecture adopting the swampland criteria.
We investigate a single field model in the context of the constant-roll inflation in which inflat... more 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 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 ≤ 0.5 at the 68% CL and Γ ≤ 0.3 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 ≤ 600 at the 68% CL and ξ ≤ 400 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.
In this paper, we use corrected $f(R)$ gravitational model which is polynomial function with a lo... more In this paper, we use corrected $f(R)$ gravitational model which is polynomial function with a logarithmic term. In that case, we employ the slow-roll condition and obtain the number of cosmological parameter. This help us to verify the swampland conjectures which is guarantee the validation of low - energy quantum field theory. The obtained results shown that the corresponding model is consistent with the swampland conjectures. Also the upper and lower limit of the parameter \textcolor{red}{$n$} are \textcolor{blue}{0.15} and \textcolor{blue}{0.0033}. Finally, by using scalar spectrum index $ n_{s} $ and tensor to scalar ratio $ r $ relations and compared with Planck 2018 empirical data, we obtain the coefficients $\alpha$,$\beta$ and $\gamma$. Also, the corresponding results are creaked by several figures, literature and also plank 2018 data.
arXiv: General Relativity and Quantum Cosmology, 2020
As we know, there is an area around the event horizon of rotating black holes, which is called by... more As we know, there is an area around the event horizon of rotating black holes, which is called by ergosphere. The corresponding rotational energy of black holes is located to this area. Every particle in this region become dragged by a rotating space-time. This makes possible to extract energy from rotating black holes, which is called the Penrose process. By using the center-of-mass energy, the Penrose process has been applied to the Kerr-Newman black hole \cite{20}. But in this paper, we examine the collision of two spinning massive particles near the corresponding black hole with critical and near-critical angular momentum. In that case, we then calculate the energy of the third particle $E_{3}$ in terms of the first two particles $E_{2}$ and $E_{1}$. We also obtain the parameter $\eta_{max}$ which is the ratio of extracted energy to input energy. We mention that here by exerting the weak gravity conjecture (WGC) we have $\eta_{max}\simeq1.5$ . We see here the WGC condition and r...
In this paper, we consider the problem of a moving heavy quark through a hot nonrelativistic, non... more In this paper, we consider the problem of a moving heavy quark through a hot nonrelativistic, non-commutative Yang-Mills plasma. We discuss about the configuration of the static and dynamic quarks, and also obtain the quasi-normal modes. 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].
Motivated by the recent works of Refs. [1, 2] where a model of inflation has been suggested with ... more Motivated by the recent works of Refs. [1, 2] where a model of inflation has been suggested with non-minimally coupled massive vector fields, we generalize their work to the study of the bouncing solution. So we consider a massive vector field, which is non-minimally coupled to gravity. Also we consider non-minimal coupling of vector field to the scalar curvature. Then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy. Finally we simply plot reconstructed physical quantities in flat universe.
In this paper we consider a quintom model of dark energy with a single scalar field T given by a ... more In this paper we consider a quintom model of dark energy with a single scalar field T given by a Lagrangian which inspired by tachyonic Lagrangian in string theory. We consider non-minimal coupling of tachyon field to the scalar curvature, then we obtain the equation of state (EoS), and the condition required for the model parameters when ω crosses over −1.
In this paper we consider a moving quark in the thermal plasma at the N =2 Supergravity theory. B... more In this paper we consider a moving quark in the thermal plasma at the N =2 Supergravity theory. By using the AdS/CFT correspondence we obtain energy loss of the quark. Then we consider the higher derivative corrections in charged AdS-black hole and calculate the drag force of the moving quark in the thermal plasma. Also we find a limit which N =2 Supergravity solutions are correspondening to the N =4 Super Yang-Mills solutions for the heavy quark.
International Journal of Theoretical Physics, 2012
In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivi... more In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivities for the R-charged black hole in STU model. We generalize previous works to the case of a black hole with three different charges. Actually we use diffusion constant to obtain ratio of shear viscosity to entropy. By applying the thermodynamical stability we recover previous results. Also we investigate the effect of higher derivative corrections.
International Journal of Theoretical Physics, 2008
In this paper, we have considered the curved universe which is filled by tachyonic field. We have... more In this paper, we have considered the curved universe which is filled by tachyonic field. We have found the exact solutions for the field, pressure, density, and scale factor and some cosmological parameters. In such universe, we have investigated the role of tachyonic field in different stages of k for the evolution of the universe. Finally we draw the graphs for the scale factor, Hubble's parameter, energy density, pressure, acceleration parameter, equation of state and potential for the different values of k. Also we obtained the exact form of field which shows that the tachyonic field has the kink form.
We study a warm inflationary model for different expansions assuming an anisotropic universe desc... more 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 fNL 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.
In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: ... more In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: see text] model by considering two different statements of shape [Formula: see text] and redshift [Formula: see text] functions. We calculate the parameters of the model including energy density [Formula: see text], tangential pressure [Formula: see text] and radial pressure [Formula: see text] for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots.
In the present work, we consider the non-minimal coupling inflationary model in the context of th... more 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.
In this paper, we impose gravitational perturbations to the static configuration of flat space-ti... more In this paper, we impose gravitational perturbations to the static configuration of flat space-time and study the stability conditions. We also investigate the presence of supersymmetry by using factorization method. In this way, by studying the shape invariance we get to the allowed frequency spectrum and also the supercharges algebra for the first time. We show that the geometric fluctuations cause unstable modes and yield the negative spectra of oscillation.
We investigate a single field model in the context of the constant-roll inflation in which inflat... more 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 Lorentzian function which is dependent on the number of e-folds in order to obtain the slow-roll parameters. We present the inflationary analysis for the model and find the observational constraints on the parameters space using the observations of CMB anisotropies 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 ≤ 0.5 at the 68% CL and Γ ≤ 0.3 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 ≤ 600 at the 68% CL and ξ ≤ 400 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.
The imaginary potential and entropic force are two important different mechanisms to characterize... more The imaginary potential and entropic force are two important different mechanisms to characterize the dissociation of heavy quarkonia. In this paper, we calculate these two quantities in strongly coupled theories with anisotropic Lifshitz scaling and hyperscaling violation exponent using holographic methods. We study how the results are affected by the hyperscaling violation parameter $$ \theta $$ θ and the dynamical exponent z at finite temperature and chemical potential. Also, we investigate the effect of the chemical potential on these quantities. As a result, we find that both mechanisms show the same results: the thermal width and the dissociation length decrease as the dynamical exponent and chemical potential increase or as the hyperscaling violating parameter decreases.
International Journal of Theoretical Physics, 2013
In this paper we consider Gödel black hole and study thermodynamics and statistics with logarithm... more In this paper we consider Gödel black hole and study thermodynamics and statistics with logarithmic correction. We calculate some important quantities such as free energy, specific heat and partition function.
We study the first-order formalism for the two coupled scalar fields with the superpotential W (φ... more We study the first-order formalism for the two coupled scalar fields with the superpotential W (φ, χ). As we know, the cosmological solution crucially depends on the coupled scalar fields. Here, we deform the corresponding superpotential and obtain the solution for some cosmological parameters. Finally, we compare the deformed and non-deformed solutions with the different figures.
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Papers by Jafar Sadeghi