arXiv subjects

Kourosh Nozari

Publications and source records attributed to Kourosh Nozari.

At least 145 records · Page 8Linked to original sources

arXiv2008

Gauss-Bonnet Cosmology with Induced Gravity and Non-Minimally Coupled Scalar Field on the Brane

We construct a cosmological model with non-minimally coupled scalar field on the brane, where Gauss-Bonnet and Induced Gravity effects are taken into account. This model has 5D character at both high and low energy limits but reduces to 4D gravity in intermediate scales. While induced gravity is a manifestation of the IR limit of the model, Gauss-Bonnet term and non-minimal coupling of scalar field and induced gravity are essentially related to UV limit of the scenario. We study cosmological implications of this scenario focusing on the late-time behavior of the solutions. In this setup, non-minimal coupling plays the role of an additional fine-tuning parameter that controls the initial density of predicted finite density big bang. Also, non-minimal coupling has important implication on the bouncing nature of the solutions.

hep-th↗

arXiv2008

Hawking Radiation as Quantum Tunneling from Noncommutative Schwarzschild Black Hole

We study tunneling process through quantum horizon of a Schwarzschild black hole in noncommutative spacetime. This is done by considering the effect of smearing of the particle mass as a Gaussian profile in flat spacetime. We show that even in this noncommutative setup there will be no correlation between the different modes of radiation which reflects the fact that information doesn't come out continuously during the evaporation process at least at late-time. However, due to spacetime noncommutativity, information might be preserved by a stable black hole remnant.

gr-qc↗

arXiv2008

Crossing of the Phantom Divided Barrier with Lorentz Invariance Violating Fields

We study possible crossing of the phantom divided barrier in a Lorentz invariance violating dark energy model. Lorentz invariance violation which is achieved by introducing a vector field in the action, incorporates directly in the dynamics of the scalar field and equation of state. This interesting feature allows us to study phantom divided barrier crossing in the context of Lorentz invariance violation. We show that for suitable choice of parameter space, equation of state can cross phantom divided barrier just by one scalar field and Lorentz violating vector field controls this crossing.

gr-qc↗

arXiv2007

Non-Minimal Inflation on the Warped DGP Brane

We construct an inflation model with inflaton non-minimally coupled to gravity on a warped DGP brane. Using an exponential potential, we calculate scalar power spectrum, spectral index and the running of the spectral index. We show that for a suitable range of non-minimal coupling it is possible to exit the inflationary phase spontaneously and without any mechanism, even in the case that minimal inflation can not exit spontaneously. By a detailed analysis of parameter space, we study the constraints imposed on the non-minimal coupling from recent observational data.

hep-th↗

arXiv2007

Non-Minimal Inflation after WMAP3

The Wilkinson Microwave Anisotropy Probe (WMAP) three year results are used to constraint non-minimal inflation models. Two different non-minimally coupled scalar field potentials are considered to calculate corresponding slow-roll parameters of non-minimal inflation. The results of numerical analysis of parameter space are compared with WMAP3 data to find appropriate new constraints on the values of the non-minimal coupling. A detailed comparison of our results with previous studies reveals the present status of the non-minimal inflation model after WMAP3.

astro-ph↗

arXiv2007

Orbits of particles in noncommutative Schwarzschild spacetime

By considering particles as smeared objects, we investigate the effects of space noncommutativity on the orbits of particles in Schwarzschild spacetime. The effects of space noncommutativity on the value of the precession of the perihelion of particle orbit and deflection of light ray in Schwarzschild geometry are calculated and the stability of circular orbits is discussed.

gr-qc↗

arXiv2007

DGP Cosmology with a Non-Minimally Coupled Scalar Field on the Brane

We construct a DGP inspired braneworld scenario where a scalar field non-minimally coupled to the induced Ricci curvature is present on the brane. First we investigate the status of gravitational potential with non-minimal coupling and observational constraints on this non-minimal model. Then we further deepen the idea of embedding of FRW cosmology in this non-minimal setup. Cosmological implications of this scenario are examined with details and the quintessence and late-time expansion of the universe within this framework are examined. Some observational constraints imposed on this non-minimal scenario are studied and relation of this model with dark radiation formalism is determined with details.

hep-th↗

arXiv2007

UV/IR Mixing and Black Hole Thermodynamics

The goal of this paper is to investigate the final stage of black hole evaporation process in the framework of Lorentz violating Modified Dispersion Relations(MDRs). As a consequence of MDRs, the high energy sector of the underlying field theory does not decouple from the low energy sector, the phenomenon which is known as UV/IR mixing. In the absence of exact supersymmetry, we derive a modified dispersion relation which shows UV/IR mixing by a novel energy dependence. Then we investigate the effects of these type of MDRs on the thermodynamics of a radiating noncommutative Schwarzschild black hole. The final stage of black hole evaporation obtained in this framework is compared with existing pictures.

gr-qc↗

arXiv2007

Embedding of FRW Cosmology in DGP Scenario with a Non-Minimally Coupled Scalar Field on the Brane

We construct a DGP inspired braneworld scenario where a scalar field non-minimally coupled to the induced Ricci curvature is present on the brane. We show that this model allows for an embedding of the standard Friedmann cosmology in the sense that the cosmological evolution of the background metric on the brane can be described by the standard Friedmann equation. The relation between our framework and the dark-energy formalism is explored.

hep-th↗

arXiv2007

Bound States and Many-Body Effects in H-Shaped Quantum Wires

In this paper, bound states energies and corresponding wave functions of H-shaped quantum wires are calculated numerically in the presence of external magnetic and electric fields and within the Landau gauge. With a suitable definition of external confinement potential, we present a numerical algorithm to calculate the profile of probability distribution of charge carriers. Our analysis shows that in the presence of external electric and magnetic fields, bound state properties of carriers are sensitive functions of an asymmetric parameter $a=\frac{W_{x}}{W_{y}}$ which measures the relative width of the well in two directions. We also study many body effect of bandgap renormalization in this quasi one dimensional system within dynamical random phase approximation.

cond-mat.str-el↗

arXiv2007

A Possible Mechanism for Production of Primordial Black Holes

Primordial Black Hole Remnants(PBHRs) can be considered as a primary source of cold dark matter. Hybrid inflation provides a possible framework for production of primordial black holes(PBHs) and these PBHs evaporate subsequently to produce PBHRs. In this paper we provide another framework for production of these PBHs. Using signature changing cosmological model and the generalized uncertainty principle as our primary inputs, first we find a geometric cosmological constant for early stage of universe evolution. This geometric cosmological constant can lead to heavy vacuum density which may be interpreted as a source of PBHs production during the inflationary phase. In the next step, since it is possible in general to have non-vanishing energy-momentum tensor for signature changing hypersurface, this non-vanishing energy-momentum tensor can be considered as a source of PBHs production. These PBHs then evaporate via the Hawking process to produce PBHRs. Finally, possible observational schemes for detecting relics of these PBHRs are discussed.

hep-th↗

arXiv2007

Thermodynamics of an Evaporating Schwarzschild Black Hole in Noncommutative Space

We investigate the effects of space noncommutativity and the generalized uncertainty principle on the thermodynamics of a radiating Schwarzschild black hole. We show that evaporation process is in such a way that black hole reaches to a maximum temperature before its final stage of evolution and then cools down to a nonsingular remnant with zero temperature and entropy. We compare our results with more reliable results of string theory. This comparison Shows that GUP and space noncommutativity are similar concepts at least from view point of black hole thermodynamics.

hep-th↗

arXiv2006

On the Stability of Planetary Circular Orbits in Noncommutative Spaces

We investigate the effects of space noncommutativity and the generalized uncertainty principle on the stability of circular orbits of particles in both a central force potential and Schwarzschild spacetime. We find noncommutative form of the effective potential which up to first order of noncommutativity parameter contains an angular momentum dependent extra term. This angular momentum dependent extra term affects the stability of circular orbits in such a way that the radius of a stable circular orbit in noncommutative space is larger than its commutative counterpart. In the case of large angular momentum, the condition for stability of circular orbits in noncommutative space differs considerably from commutative case.

gr-qc↗

arXiv2006

Reissner-Nordström Black Hole Thermodynamics in Noncommutative Spaces

This paper considers the effects of space noncommutativity on the thermodynamics of a Reissner-Nordström black hole. In the first step, we extend the ordinary formalism of Bekenstein-Hawking to the case of charged black holes in commutative space. In the second step we investigate the effects of space noncommutativity and the generalized uncertainty principle on the thermodynamics of charged black holes. Finally we compare thermodynamics of charged black holes in commutative space with thermodynamics of Schwarzschild black hole in noncommutative space. In this comparison we explore some conceptual relation between charge and space noncommutativity.

gr-qc↗

arXiv2006

Loop Quantum Gravity Modification of the Compton Effect

Modified dispersion relations(MDRs) as a manifestation of Lorentz invariance violation, have been appeared in alternative approaches to quantum gravity problem. Loop quantum gravity is one of these approaches which evidently requires modification of dispersion relations. These MDRs will affect the usual formulation of the Compton effect. The purpose of this paper is to incorporate the effects of loop quantum gravity MDRs on the formulation of Compton scattering. Using limitations imposed on MDRs parameters from Ultra High Energy Cosmic Rays(UHECR), we estimate the quantum gravity-induced wavelength shift of scattered photons in a typical Compton process. Possible experimental detection of this wavelength shift will provide strong support for underlying quantum gravity proposal.

gr-qc↗

arXiv2006

Implications of Minimal Length Scale on the Statistical Mechanics of Ideal Gas

Several alternative approaches to quantum gravity problem suggest the modification of the {\it fundamental volume $ω_{0}$} of the accessible phase space for representative points. This modified fundamental volume has a novel momentum dependence. In this paper, we study the effects of this modification on the thermodynamics of an ideal gas within the microcanonical ensemble and using the generalized uncertainty principle(GUP). Although the induced modifications are important only in quantum gravity era, possible experimental manifestation of these effects may provides strong support for underlying quantum gravity proposal.

hep-th↗

arXiv2006

Failure of Standard Thermodynamics in Planck Scale Black Hole System

The final stage of the black hole evaporation is a matter of debates in the existing literature. In this paper, we consider this problem within two alternative approaches: noncommutative geometry(NCG) and the generalized uncertainty principle(GUP). We compare the results of two scenarios to find a relation between parameters of these approaches. Our results show some extraordinary thermodynamical behavior for Planck size black hole evaporation. These extraordinary behavior may reflect the need for a fractal nonextensive thermodynamics for Planck size black hole evaporation process.

hep-th↗

arXiv2006

Can Quantum Gravitational Effects Manifest themselves at Large Distances?

Consider a proposed model of the universe with $\hbar$ much greater than its well-known value of $10^{-34} Js$. In this model universe, very large objects can show quantum behaviors. In a scenario with large extra dimensions, $\hbar$ can attains very large values depending on the dimensionality of spacetime. In this letter, we show that although conventional thinking indicates that quantum gravitational effects should manifest themselves only at very small scales, in actuality quantum gravitational effects can manifest themselves at large scales too. We use the generalized uncertainty principle with a non-zero minimal uncertainty in momentum as our primary input to construct a mathematical framework for our proposal.

hep-th↗