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H. Mohseni Sadjadi

Publications and source records attributed to H. Mohseni Sadjadi.

67 records · Page 4Linked to original sources
arXiv2007

Particle vs. future event horizon in interacting holographic dark energy model

By choosing the future event horizon as the horizon of the flat FLRW universe, we show that although the interacting holographic dark energy model is able to explain the phantom divide line crossing, but the thermodynamics second law is not respected in this model. We show that if one takes the particle event horizon as the horizon of the universe, besides describing $ω=-1$ crossing in a consistent way with thermodynamics second law, he is able to determine appropriately the ratio of dark matter to dark energy density at transition time. In this approach, after the first transition from quintessence to phantom, there is another transition from phantom to quintessence phase which avoids the big rip singularity.

gr-qc↗
arXiv2006

Schwarzschild black hole and the generalized second law in phantom-dominated universe

We study the conditions required for validity of the generalized second law in phantom dominated universe in the presence of Schwarzschild black hole. Our study is independent of the origin of the phantom like behavior of the considered universe. We also discuss the generalized second law in the neighborhood of transition (from quintessence to phantom regime) time. We show that even for a constant equation of state parameter the generalized second law may be satisfied provided the temperature is not taken as de Sitter temperature. It is shown that in models with (only) a transition from quintessence to phantom regime the generalized second law does not hold in the transition epoch.

gr-qc↗
arXiv2006

Cosmological coincidence problem in interacting dark energy models

An interacting dark energy model with interaction term $Q= λ_m Hρ_m+λ_dHρ_d$ is considered. By studying the model near the transition time, in which the system crosses the w=-1 phantom-divide-line, the conditions needed to overcome the coincidence problem is investigated. The phantom model, as a candidate for dark energy, is considered and for two specific examples, the quadratic and exponential phantom potentials, it is shown that it is possible the system crosses the w=-1 line, meanwhile the coincidence problem is alleviated, the two facts that have root in observations.

gr-qc↗
arXiv2006

Transition from quintessence to phantom phase in quintom model

Assuming the Hubble parameter is a continuous and differentiable function of comoving time, we investigate necessary conditions for quintessence to phantom phase transition in quintom model. For power-law and exponential potential examples, we study the behavior of dynamical dark energy fields and Hubble parameter near the transition time, and show that the phantom-divide-line w=-1 is crossed in these models.

gr-qc↗
arXiv2006

The effect of geometry on charge confinement in three dimensions

We show that, in contrast to the flat case, the Maxwell theory is not confining in the background of the three dimensional BTZ black-hole (covering space). We also study the effect of the curvature on screening behavior of Maxwell-Chern-Simons model in this space-time.

gr-qc↗
arXiv2006

Attractor solutions for general hessence dark energy

As a candidate for the dark energy, the hessence model has been recently introduced. We discuss the critical points of this model in almost general case, that is for arbitrary hessence potential and almost arbitrary hessence-background matter interaction. It is shown that in all models, there always exist some stable late-time attractors. It is shown that our general results coincide with those solutions obtained earlier for special cases, but some of them are new. These new solutions have two unique characteristics. First the hessence field has finite value in these solutions and second, their stabilities depend on the second derivative of the hessence potential.

hep-th↗
arXiv2005

Electrostatic self-energy and Bekenstein entropy bound in the massive Schwinger model

We obtain the electrostatic energy of two opposite charges near the horizon of stationary black-holes in the massive Schwinger model. Besides the confining aspects of the model, we discuss the Bekenstein entropy upper bound of a charged object using the generalized second law. We show that despite the massless case, in the massive Schwinger model the entropy of the black hole and consequently the Bekenstein bound are altered by the vacuum polarization.

gr-qc↗
arXiv2003

Electrostatic self-energy in QED_2 on curved background

By considering the vacuum polarization, we study the effects of geometry on electrostatic self--energy of a test charge near the black hole horizon and also in regions with strong and weak curvature in static two dimensional curved backgrounds. We also discuss the relation of ultraviolet behavior of the gauge field propagator and charge confinement.

hep-th↗
arXiv2001

Massive Schwinger model and its confining aspects on curved space-time

Using a covariant method to regularize the composite operators, we obtain the bosonized action of the massive Schwinger model on a classical curved background. Using the solution of the bosonic effective action, the energy of two static external charges with finite and large distance separation on a static curved space-time is obtained. The confining behavior of this model is also explicitly discussed.

hep-th↗
arXiv2000

Confinement and screening of the Schwinger model on the Poincare half plane

We discuss the confining features of the Schwinger model on the Poincare half plane. We show that despite the fact that the expectation value of the large Wilson loop of massless Schwinger model displays the perimeter behavior, the system can be in confining phase due to the singularity of the metric at horizontal axis. It is also shown that in the quenched Schwinger model, the area dependence of the Wilson loop, in contrast to the flat case, is a not a sign of confinement and the model has a finite energy even for large external charges separation. The presence of dynamical fermions can not modify the screening or the confining behavior of the system. Finally we show that in the massive Schwinger model, the system is again in screening phase. The zero curvature limit of the solutions is also discussed.

hep-th↗
arXiv1999

Coulomb gas representation of quantum Hall effect on Riemann surfaces

Using the correlation function of chiral vertex operators of the Coulomb gas model, we find the Laughlin wavefunctions of quantum Hall effect, with filling factor $ν=1/m$, on Riemann sufaces with Poincare metric. The same is done for quasihole wavefunctions. We also discuss their plasma analogy.

hep-th↗
arXiv1996

Laughlin states on the Poincare half-plane and its quantum group symmetry

We find the Laughlin states of the electrons on the Poincare half-plane in different representations. In each case we show that there exist a quantum group $su_q(2)$ symmetry such that the Laughlin states are a representation of it. We calculate the corresponding filling factor by using the plasma analogy of the FQHE.

hep-th↗