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A. Jahan

Publications and source records attributed to A. Jahan.

At least 19 recordsLinked to original sources
arXiv2020

The Lamb Problem with a Nonuniform String

The time evolution of an oscillator coupled to an infinite string with a discontinuous mass density is investigated. It is shown that the equation of motion of the oscillator leads to a nonlinear characteristic equation due to the frequency-dependent nature of the point impedance of the string. Then, the method of perturbation theory is applied to solve the characteristic equation to first order in perturbation parameter. Finally, response of the oscillator to an impulse is obtained by means of the Green's function method.

physics.class-ph↗
arXiv2019

Casimir energy of an open string with angle-dependent boundary condition

We consider an open string with ends laying on the two different solid beams (rods). This set-up is equivalent to two scalar fields with a set of constraints at their end-points. We calculate the zero-point energy and the Casimir energy in three different ways: (1) by use of the Hurwitz zeta function, (2) by employing the contour integration method in the complex frequency plane, and (3) by constructing the Green's function for the system. In the case of contour integration we also present a finite temperature expression for the Casimir energy, along with a convenient analytic approximation for high temperatures. The Casimir energy at zero temperature is found to be a sum of the Luscher potential energy and a term depending on the angle between the beams. The relationship of this model to an analogous open string model with charges fixed at its ends, moving in an electromagnetic field, is discussed.

hep-th↗
arXiv2018

Vacuum Energy of a Non-relativistic String with Nontrivial Boundary Condition

We derive the partition function of a non-relativistic quantum string which its ends are allowed to freely slide on the two angled straight solid rods. We first derive the classical solution of the model and then use it to derive the partition function utilizing the path integral method. We show that the vacuum energy is sum of the Luscher potential plus a term which depends on the relative angle between rods.

hep-th↗
arXiv2018

Vacuum Persistence Amplitude and Gravitational Potential in $f(R)$ Gravity

The source theory provides a straightforward way to obtain the Newton's potential upon establishing the vacuum-to-vacuum transition amplitude in quantized Einstein theory of gravity. Here, we use the same method to derive the gravitational potential of two static point masses in $f(R)=R+aR^2$ gravity.

hep-th↗
arXiv2017

Thermodynamic analysis of gravitational field equations in Lyra manifold

Considering the Einstein field equations in Lyra manifold, and applying the unified first law of thermodynamics as well as the Clausius relation to the apparent horizon of FRW universe, we find the entropy of apparent horizon in Lyra manifold. In addition, the validity of second law of thermodynamics and its generalized form are also studied. Finally, we use the first law of thermodynamics in order to find the horizon entropy of static spherically symmetric spacetimes. Some results of considering (anti)de-Sitter and Schwarzschild metrics have also been addressed.

gr-qc↗
arXiv2016

Gravitational luminosity of a hot plasma in R^2 gravity

The R^{2}-gravity contribution to energy loss of a hot plasma due to the gravitational bremsstrahlung is calculated in the linearized theory on the basis of classical Coulomb scattering of plasma constituents in small-angle scattering approximation. The explicit dependence of the gravitational luminosity on the plasma temperature is derived and its relevance to the Einstein gravity is demonstrated. The result when applied to the Sun as a hot plasma, shows very good agreement with available data.

gr-qc↗
arXiv2016

Anharmonic Noncommutative Oscillator at Finite Temperature

Classical and quantum anharmonic noncommutative oscillators with quartic self-interacting potential are considered and the effect of self-interaction term on the free energy and partition function of both models is calculated to first order in coupling constant.

hep-th↗
arXiv2015

Partition Function of the Harmonic Oscillator on a Noncommutative Plane

We derive the partition function of the one-body and two-body systems of classical noncommutative harmonic oscillator in two dimensions. Then, we employ the path integral approach to the quantum noncommutative harmonic oscillator and derive the partition function of the both systems at finite temperature.

hep-th↗
arXiv2014

Gravitational Radiation in Noncommutative Gravity

The gravitational radiation power of a binary system in a noncommutative space is derived and it's rate of the period decrease is calculated to first order in noncommutativity parameter. By comparing the theoretical results with the observational data of the binary pulsar PSR 1913+16, we find a bound on the noncommutativity parameter.

gr-qc↗
arXiv2013

On Gravitational Radiation by a Quantum Bound System

A method based on the path integral approach is engaged to consider the gravitational emission from a quantum mechanical bound system in a locally inertial frame. In such a frame, interaction between the electromagnetic (bound potential) and gravitational fields can be neglected resulting in the less mathematical complexity. The final outcome is in agreement with the previous result for the radiation intensity of emitted gravitons due to decay of bound states in TT gauge.

gr-qc↗
arXiv2012

Cosmological Implications of a Lorentz Invariance Violating O(2) Model

We derive the free energy of a Lorentz invariance violating (LIV) O(2) model, for which a non-vanishing commutator among it's momenta is supposed. Then we investigate the possible implications of such a matter field on the time evolution of a flat FRW universe at low and high temperatures.

hep-th↗
arXiv2012

Scalar-Graviton Scattering in Noncommutative Space and Deformed Newton Gravity

The isotropy of Newton potential in noncommutative space disappears as it deforms to a momentum dependent one. We generalize the earlier derivation of such a deformed potential to the relativistic regime by calculating the 2 scalar-1 graviton scattering amplitude by taking into account the noncommutativity of space.

hep-th↗
arXiv2010

On the String Pair Creation in Dp-Dp' Brane System

We address the bosonic string pair creation in a system of parallel Dp-Dp' (p<p') branes by applying the path integral formalism. We drive the string pair creation rate by calculating the one loop vacuum amplitude of the setup in presence of the background electric field defined over the Dp'-brane. It is pointed out that just the components of the electric field defined over the $p$ spatial directions (the common directions along which the both D-branes are extended) give rise to the pair creation

hep-th↗