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Kourosh Nozari

Publications and source records attributed to Kourosh Nozari.

At least 91 records · Page 5Linked to original sources
arXiv2013

Energy conditions in $F(T,Θ)$ gravity and compatibility with a stable de Sitter solution

We study a new type of the modified teleparallel gravity of the form $F(T,\,Θ)$ in which $T$, the torsion scalar, is coupled with $Θ$, the trace of the stress-energy tensor. In a perturbational approach, we study the stability of the solutions and as a special case we find a condition for stability of the de Sitter phase. Then we adopt a suitable form for $F(T,Θ)$ that realizes a stable de Sitter solution so that the stability condition creates a specific constraint on the parametric space of the model. Finally, the energy conditions in the framework of $F(T,Θ)$ gravity is investigated.

gr-qc↗
arXiv2013

Non-Minimal Braneworld Inflation after the Planck

The recently released Planck data have constrained 4-dimensional inflationary parameters even more accurately than ever. We consider an extension of the braneworld model with induced gravity and a non-minimally coupled scalar field on the brane. We constraint the inflation parameters in this setup, by adopting six types of potential, in confrontation with the joint Planck+WMAP9+BAO data. We show that a potential of the type $V(φ)=V_{0}\exp(-βφ)$ has the best fit with newly released observational data.

astro-ph.CO↗
arXiv2013

Some Aspects of Supersymmetric Field Theories with Minimal Length and Maximal Momentum

We consider a real scalar field and a Majorana fermion field to construct a supersymmetric quantum theory of free fermion fields based on the deformed Heisenberg algebra $[x,p]=i\hbar\big(1-βp+2β^{2}p^{2}\big)$, where $β$ is a deformation parameter. We present a deformed supersymmetric algebra in the presence of minimal length and maximal momentum.

hep-th↗
arXiv2013

Cosmological dynamics of a non-minimally coupled bulk scalar field in DGP setup

We consider cosmological dynamics of a canonical bulk scalar field, which is coupled non-minimally to 5-dimensional Ricci scalar in a DGP setup. We show that presence of this non-minimally coupled bulk scalar field affects the jump conditions of the original DGP model significantly. Within a superpotential approach, we perform some numerical analysis of the model parameter space and consider bulk-brane energy exchange in this setup. Also we show that the normal, ghost-free branch of the DGP solutions in this case has the potential to realize a self-consistent phantom-like behavior and therefore explains late time acceleration of the universe in a consistent way.

gr-qc↗
arXiv2013

Gauss-Bonnet Braneworld Cosmology with Modified Induced Gravity on the Brane

We analyze the background cosmology for an extension of the DGP gravity with Gauss-Bonnet term in the bulk and $f(R)$ gravity on the brane. We investigate implications of this setup on the late-time cosmic history. Within a dynamical system approach, we study cosmological dynamics of this setup focusing on the role played by curvature effects. Finally we constraint the parameters of the model by confrontation with recent observational data.

gr-qc↗
arXiv2013

Some Aspects of Tachyon Field Cosmology

We study inflation, perturbations, non-gaussinity and late-time cosmological dynamics of a tachyon field both minimally and non-minimally coupled to gravity. By analyzing the parameters space of the model, the viability of the model in confrontation with recent observational data is considered. In a dynamical system technique, we study the phase space dynamics of both minimally and non-minimally coupled tachyon field. We find the fixed points (lines in our setup) and explore their stability. Also, we perform a statefinder diagnostic to both cases and show that the trajectories of the state finder pairs reach a stable state which is corresponding to a $Λ$CDM scenario.

gr-qc↗
arXiv2013

Cosmological dynamics of a hybrid chameleon scenario

We consider a hybrid scalar field which is non-minimally coupled to the matter and models a chameleon cosmology. By introducing an effective potential, we study the dependence of the effective potential's minimum and hybrid chameleon field's masses to the local matter density. In a dynamical system technique, we analyze the phase space of this two-field chameleon model, find its fixed points and study their stability. We show that the hybrid chameleon domination solution is a stable attractor and the universe in this setup experiences a phantom divide crossing.

gr-qc↗
arXiv2012

Braneworld Teleparallel Gravity

We study the gravity in the context of a braneworld teleparallel scenario. The geometrical setup is assumed to be Randall-Sundrum II model where a single positive tension brane is embedded in an infinite AdS bulk. We derive the equivalent of Gauss-Codacci equations in teleparallel gravity and junction conditions in this setup. Using these results we derive the induced teleparallel field equations on the brane. We show that compared to general relativity, the induced field equations in teleparallel gravity contain two extra terms arising from the extra degrees of freedom in the teleparallel Lagrangian. The term carrying the effects of the bulk to the brane is also calculated and its implications are discussed.

gr-qc↗
arXiv2012

Natural Cutoffs and Quantum Tunneling from Black Hole Horizon

We study tunneling of massless particles through quantum horizon of a Schwarzschild black hole where quantum gravity effects are taken into account. These effects are encoded in the existence of natural cutoffs as a minimal length, a minimal momentum and a maximal momentum through a generalized uncertainty principle. We study possible correlations between emitted particles to address the information loss problem. We focus also on the role played by these natural cutoffs on the tunneling rate through quantum horizon.

hep-th↗
arXiv2012

Stability analysis of the cosmological solutions with induced gravity and scalar field on the brane

We study cosmological dynamics and phase space of a scalar field localized on the DGP brane. We consider both the minimally and nonminimally coupled scalar quintessence and phantom fields on the brane. In the nonminimal case, the scalar field couples with induced gravity on the brane. We present a detailed analysis of the critical points, their stability and late-time cosmological viability of the solutions in the phase space of the model.

gr-qc↗
arXiv2012

Generalized Uncertainty Principle and the Ramsauer-Townsend Effect

The scattering cross section of electrons in noble gas atoms exhibits a minimum value at electron energies of approximately 1eV. This is the Ramsauer-Townsend effect. In this letter, we study the Ramsauer-Townsend effect in the framework of the Generalized Uncertainty Principle.

gr-qc↗
arXiv2012

Braneworld non-minimal inflation with induced gravity

We study cosmological inflation on a warped DGP braneworld where inflaton field is non-minimally coupled to induced gravity on the brane. We present a detailed calculation of the perturbations and inflation parameters both in Jordan and Einstein frame. We analyze the parameters space of the model fully to justify about the viability of the model in confrontation with recent observational data. We compare the results obtained in these two frames also in order to judge which frame gives more acceptable results in comparison with observational data.

gr-qc↗
arXiv2012

Tunneling of massive and charged particles from noncommutative Reissner-Nordström black hole

Massive charged and uncharged particles tunneling from commutative Reissner-Nordstrom black hole horizon has been studied with details in literature. Here, by adopting the coherent state picture of spacetime noncommutativity, we study tunneling of massive and charged particles from a noncommutative inspired Reissner-Nordstrom black hole horizon. We show that Hawking radiation in this case is not purely thermal and there are correlations between emitted modes. These correlations may provide a solution to the information loss problem. We also study thermodynamics of noncommutative horizon in this setup.

gr-qc↗
arXiv2012

Minimal length, maximal momentum and Hilbert space representation of quantum mechanics

Kempf et al. in Ref. [1] have formulated a Hilbert space representation of quantum mechanics with a minimal measurable length. Recently it has been revealed, in the context of doubly special relativity, that a test particles' momentum cannot be arbitrarily imprecise and therefore there is an upper bound for momentum fluctuations. Taking this achievement into account, we generalize the seminal work of Kempf {\it et al.} to the case that there is also a maximal particles' momentum. Existence of an upper bound for the test particles' momentum provides several novel and interesting features, some of which are studied in this paper.

hep-th↗
arXiv2012

On the dissipative non-minimal braneworld inflation

We study the effects of the non-minimal coupling on the dissipative dynamics of the warm inflation in a braneworld setup, where the inflaton field is non-minimally coupled to induced gravity on the warped DGP brane. We study with details the effects of the non-minimal coupling and dissipation on the inflationary dynamics on the normal DGP branch of this scenario in the high-dissipation and high-energy regime. We show that incorporation of the non-minimal coupling in this setup decreases the number of e-folds relative to the minimal case. We also compare our model parameters with recent observational data.

gr-qc↗
arXiv2012

Cosmological braneworld solutions with bulk scalar field in DGP setup

We study cosmological dynamics of a canonical bulk scalar field in the DGP setup within a superpotential approach. We show that the normal branch of this DGP-inspired model realizes a late-time de Sitter expansion on the brane. We extend this study to the case that the bulk contains a phantom scalar field. Our detailed study in the supergravity-style analysis reveals some yet unexplored aspects of cosmological dynamics of bulk scalar field in the normal DGP setup. Some clarifying examples along with numerical analysis of the model parameter space are presented in each case.

gr-qc↗
arXiv2012

Cosmological dynamics with modified induced gravity on the normal DGP branch

In this paper we investigate cosmological dynamics on the normal branch of a DGP-inspired scenario within a phase space approach where induced gravity is modified in the spirit of $f(R)$-theories. We apply the dynamical system analysis to achieve the stable solutions of the scenario in the normal DGP branch. Firstly, we consider a general form of the modified induced gravity and we show that there is a standard de Sitter point in phase space of the model. Then we prove that this point is stable attractor only for those $f(R)$ functions that account for late-time cosmic speed-up.

gr-qc↗