arXiv subjects

E. Mahichi

Publications and source records attributed to E. Mahichi.

4 recordsLinked to original sources

arXiv2023

Cosmological Evolution, Analytical Parametrization, and Dynamical Stability of a Bouncing Universe in Non-Minimal Kinetic Coupling Gravity

In this paper, the bouncing cosmology is studied in the framework of the non-minimal kinetic coupling theory between the scalar field and the Einstein tensor. After deriving the modified Friedmann equations and the field equation, by applying the Bounce condition, the system of equations is solved numerically without assuming any analytical form for the scale factor. Thus, the time evolution of the scale factor, the scalar field, and other cosmological quantities are obtained directly from the model dynamics. Then, in order to provide an explicit form for the cosmic evolution, an analytical parameterization for the scale factor is introduced, which is fitted to the numerical solution with high accuracy and its validity is confirmed by comparing the Hubble parameter obtained from the parameterization with the numerical solution. Using this framework, the behavior of cosmological parameters including the Hubble parameter, the comoving Hubble horizon, the energy density, the pressure, and the equation of state (EoS) parameter during the evolution of the universe is investigated, and a smooth transition from the contraction phase to the expansion phase without the occurrence of a singularity is shown. Next, the stability of the model is studied using an autonomous dynamical system and critical point analysis in phase space. The results show that the presented model, in addition to describing a non-singular bouncing scenario, has stable dynamic behavior and the introduced analytical parameterization can be used as a suitable tool for future analytical studies.

gr-qc↗

arXiv2023

The interaction of extended Bose-Einstein condensate dark matter with viscous $f(T, B)$ gravity

In this paper, we study the viscous $f(T, B)$ gravity model as a source of dark energy, and the Extended Bose-Einstein Condensate (EBEC) as a source of dark matter, in a flat-FRW metric. In the presence of bulk viscosity, we obtain Friedmann equations and write two continuity equations of dark energy and dark matter by interacting them. Using the generalized Gross-Pitaeveskii equation, we earn Equation of State (EoS) of dark matter by EBEC regime as $p_m = αρ_{m} + βρ_{m}^2$ in which the both of terms are respectively introduced as normal dark matter and dark matter halo. The innovation of the work is that we can simultaneously describe the nature of the dark parts of the universe with the viscous $f(T, B)$ gravity and the EBEC regime, which leads to a deep understanding of the different epochs of the universe from early to late times. In what follows, the energy density and the pressure of dark energy are reconstructed in terms of the redshift parameter, and then we fit the obtained results with 53 supernova data from the Hubble data constraints. Next, we plot the cosmological parameters in terms of the redshift parameter and conclude that the current universe is in an accelerated phase. Finally, we analyze the stability and instability of the current model with the sound speed parameter as well as we draw the density parameter values for dark energy in terms of the redshift parameter.

gr-qc↗

arXiv2021

Extended Bose-Einstein condensate dark matter in viscous Gauss-Bonnet gravity

In this paper, we study the $F(R, G)$ gravity model with an interacting model by flat-FRW metric in a viscous fluid. We consider that the universe dominates with components of dark matter and dark energy. This means that the dark matter component derives from Extended Bose-Einstein Condensate (EBEC) and the components of dark energy arise from the $F(R, G)$ gravity. After obtaining the Einstein equation, the energy density and the pressure of dark energy are written in terms of the geometries of the curvature and the Gauss-Bonnet terms, and components of dark matter and viscous fluid. Also, the corresponding continuity equations are written with the presence of interaction terms. In what follows, we employ the EBEC regime instead of the normal dark matter by the dark matter Equation of State (EoS) as $p_{dm} = αρ_{dm} + βρ_{dm}^2$, which arises from the gravitational form. The EoS can be expressed from the perspective of the virial expansion, in which the first and second terms represent normal dark matter and quantum ground state. Next, the corresponding Friedmann equations reconstruct in terms of the redshift parameter, then by using the scenario of the power-law cosmology for the scale factor, we fit the present model with the Hubble amounts of 51 supernova data by the likelihood analysis. In that case, we acquire the cosmological parameters of dark energy in terms of the redshift parameter, and by plotting these graphs, we see that the universe is currently undergoing an accelerated expansion phase. Finally, we investigate the stability of the present model with the sound speed parameter.

gr-qc↗

arXiv2021

Viscous interacting and stability on dark matter Bose-Einstein condensation with modified Chaplygin gas

In this paper, the viscous cosmological dynamics are studied in the presence of dark matter Bose-Einstein Condensation (BEC) by curved-FRW background. For this purpose, we use the BEC regime rather than the normal dark matter (the cold dark matter or the barotropic dark matter) with the dark matter Equation of State (EoS) as $p_{dm} \propto ρ_{dm}^2$, which arises from the gravitational form. Therefore, we obtain the corresponding continuity equations with the existence of the universe components by considering an interacting model with modified Chaplygin gas. Afterward, we derive the energy density and the pressure of dark energy in terms of the redshift parameter. And then, by introducing a parametrization function and fitting it with 51 supernova data with the likelihood analysis, we find the cosmological parameters versus redshift parameter. In what follows, we plot the corresponding dynamic graphs proportional to redshift, and then we represent the universe is currently undergoing an accelerated expansion phase. Finally, we explore the stability and the instability of the present model with the sound speed parameter.

gr-qc↗