2020-02-28T00:03:27Z
http://ijaa.du.ac.ir/?_action=export&rf=summon&issue=39
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2019
6
1
The phase transition of corrected black hole with f(R) gravity
Mohammad
Rostami
Jafar
Sadeghi
Sedigheh
Mirabotalebi
Ami ali
Masoudi
In this letter, we consider static black hole in f(R) gravity.<br />We take advantage from corrected entropy and temperature and investigate such black hole. Finally, we study the $ P - V $ critically and phase transition of corrected black hole with respect to entropy and temperature. Here also, we obtain the heat capacity for the static black hole in $ f(R) $ gravity. This calculation help us to investigate some singularity.<br />We have shown that the corrections exist for any black hole, but they are important for a small black holes and negligible for the large black holes. The advantage of a static black hole in $ f(R) $ gravity is its holographic picture, which is a van der Waals fluid. Then, We have shown that in the presence of corrections there is still a van der Waals fluid as a dual picture.<br />The critical values of event horizon radius for phase transitions are shown due to the corrections of entropy and temperature.<br />We have some figures which show the phase transition and $ P - V $ critically.
The static black hole
Phase transition
Van der Waals behavior
corrected of entropy and temperature
2019
03
01
1
8
http://ijaa.du.ac.ir/article_152_e26cb129b4163749762fc63251538928.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2019
6
1
Different Magnetic Field Distributions in Deformed Neutron Stars
Mina
Zamani
Mohsen
Bigdeli
In this work, we review the formalism which would allow us to model magnetically deformed neutron stars. We study the effect of different magnetic field configurations on the equation of state (EoS) and the structure of such stars. For this aim, the EoS of magnetars is acquired by using the lowest order constraint variational (LOCV) method and employing the AV<sub>18</sub> potential. <br />We show how the magnetic field varies from the surface to the center of neutron star by using various exponential and polynomial profiles and compare their results.<br />In addition, global properties of neutron stars are obtained within two formalisms. The first formalism is described by considering the pressure into two directions and the deformation of neutron stars is governed by anisotropies in the equation of state. The second formalism for investigating macroscopic properties of magnetars is gained by treating the nonuniform pressure as a perturbation to the total pressure and expanding metric and pressure up to the quadrupole term in spherical harmonics.<br />Afterwards, we include three nucleon interactions (TNI) to the EoS and apply this model to represent our results for both exponential and polynomial magnetic field profiles.<br />The maximum gravitational mass is obtained in the range of (1.71-1.80) M<sub>.</sub> and (2.13-2.19) M<sub>.</sub> for the EoS without and with TNI contribution, respectively.
magnetars
magnetic field profiles
deformed neutron stars
2019
03
01
9
23
http://ijaa.du.ac.ir/article_159_92c75c51107559c39303a2ef3b4d7369.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2019
6
1
Super algebra and Harmonic Oscillator in Anti de Sitter space
Omid
Jalili
Shahin
Toni
The harmonic oscillator in anti de Sitter space(AdS) is discussed. We consider the harmonic oscillator potential and then time independent Schrodinger equation in AdS space. Then we apply the supersymmetric Quantum Mechanics approach to solve our differential equation. In this paper we have solved Schrodinger equation for harmonic oscillator in AdS spacetime by supersymmetry approach. The shape invariance, charge conjugation and other properties of supersymmetric Quantum Mechanics for our equation are discussed. We investigate the dynamical symmetry into definite group. We also obtain the Casimir operator and thermodynamics properties of harmonic oscillator in Anti de sitter space. We have discussed the corresponding algebra for the N=2 Supersymmetry. The energy spectrum of the harmonic oscillator is similar to the flat space but the constant terms of it are different, This constant terms depends to the geometrical parameter of the background. Finally we have obtained the various thermodynamics quantity of the system.
Harmonic Oscillator
Anti de Sitter space
Supersymmetry
Thermal Properties
2019
03
01
25
31
http://ijaa.du.ac.ir/article_158_465bf23f88d017cffb70b0efc35f50d7.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2019
6
1
Bulk Viscous Bianchi Type VI0 Cosmological Model in the Self-creation Theory of Gravitation and in the General Theory of Relativity
E. A.
Hegazy
In the second self-creation theory of gravitation and in the general theory of relativity, Bianchi type VI<sub>0</sub> cosmological model in the presence of viscous fluid is studied. An exact solution of the field equations is given by considering the cosmological model yields a constant decelerations parameter q=constant and the coefficients of the metric are taken as A(t)=[c<sub>1</sub>t+c<sub>2</sub>]3L/(q+1)(L+1), B(t)=[c<sub>1</sub>t+c<sub>2</sub>]3/2(q+1)(L+1),C(t)=[c<sub>1</sub> t+ c<sub>2</sub>]3/2(q+1)(L+1),where c<sub>1</sub>,c<sub>2</sub> and L are constants . Effect of the viscosity on the entropy of the universe is given by a composition of the second law of thermodynamics with the the energy momentum tensor T<sub>j</sub><sup>i</sup> with bulk viscous term in a conservative manner. We obtained a formula for calculation the entropy of the universe in term of the viscosity and used it to study and compare the Entropy, Enthalpy, Gibbs energy and Helmholtz energy of the universe in the presence of viscosity term in the self-creation theory of gravitation and in the general theory of relativity. The physical and geometrical properties of the obtained models are discussed.
General theory of relativity
Einstein field equations
Bianchi type VI$_0$ cosmological models
Viscosity
Entropy
2019
03
01
33
44
http://ijaa.du.ac.ir/article_160_2327cc011977eef2cc5a380d82267e83.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2019
6
1
The braneworld stability and large-scale correction in graphene like background
Zahra
Zali
Jafar
Sadeghi
Behnam
Pourhassan
In this work, we consider a graphene-like background in braneworld scenario which is one of the interesting models in cosmology and theoretical physics. Indeed, this paper is an application of holography in condense matter. We use the geometric form of potential which help to obtain field equations and solve it to obtain the energy spectrum. In that case we calculate superpotential and energy density of this model. Thermodynamical study of this model suggest that the entropy should modified due to the large-scale corrections. An important point is stability of this model in braneworld scenario. We study model stability by two separated methods. We calculate heat capacity, Gibbs and Helmholtz free energy to analyze thermodynamics stability, then consider small perturbations in graphene like metric background to investigate gravitational stability. We find that the model is completely stable unless in very low temperatures where the graphene structure may break. Hence, we confirm that our braneworld model is thermodynamically stable and also small perturbations yields to an oscillation around the equilibrium point.
stability
Perturbations
Graphene
Thermodynamics
Braneworld
2019
03
01
45
52
http://ijaa.du.ac.ir/article_161_c007483ab819d8239d4e44a9118b8656.pdf