Abdulla Al Mamon

In this paper, we examine a cosmological model with a new parametrization of the dark energy equation of state using a single parameter, [ ], to measure departures from the typical [ ]CDM case. The growth rate of cosmic structure and the statefinder hierarchy is used as diagnostics to analyze the model. A [ ] analysis is also performed, in which [ ] represents the dark energy equation of state parameter and the prime signifies differentiation with regard to [ ], where [ ] is the scale factor. We also investigate the evolution of the apparent magnitude and the Hubble parameter, contrasting the model’s predictions with those of [ ]CDM and with observable data from Type Ia Supernovae and Hubble parameter observations. We find that the cosmos accelerates after decelerating in the recent cosmic past, but does not asymptotically approach a de Sitter phase in the far future as does the classic [ ]CDM model. Rather, a second transition — from acceleration to deceleration — is what the model anticipates. Last, as a diagnostic of the model’s behavior under minor perturbations, we evaluate the squared sound speed to determine the dynamical stability of the model.

This paper presents an investigation of cosmological dynamics of tachyon fluid coupled to varying-mass dark matter particles in the background of spatially flat FLRW universe. The mechanism of varying mass particles scenario assumes the mass of the dark matter depends on time ‘t’ through the scalar field ϕ in the sense that the decaying of dark matter reproduces the scalar field. First, we analyze the model from dynamical systems perspective by converting the cosmological evolution equations into an autonomous system of ordinary differential equations with a suitable transformation of variables. We choose the mass of dark matter as exponential function of scalar field and the exponential potential of the tachyon field is undertaken in such a way that the autonomous system is reduced in three dimensional form. The critical points obtained from the system are non-hyperbolic in nature. The center manifold theory is employed to discuss the nature of the critical points. Numerical investigation also carried out for some critical points. From this analysis, we obtain dust dominated decelerated transient phase of the Universe followed by dark energy dominated scaling attractor alleviating the coincidence problem. Next, we perform the statefinder diagnostic approach to compare our model to ΛCDM and finally we study the evolution of the Hubble parameter and the distance modulus and compare this with observational data.

In this paper, we investigate a non-canonical scalar field model in the background dynamics of anisotropic Locally Rotationally Symmetric (LRS) Bianchi type I universe where gravity is coupled minimally to scalar field which is taken as dark energy and pressureless dust as dark matter are the main matter content of the universe. We perform dynamical system analysis to characterize the cosmological evolution of the model with and without interaction in the dark sector separately. First, we convert the evolution equation into an autonomous system of ordinary differential equations by using a suitable choice of dimensionless variables, which are normalized over the Hubble scale. We choose scalar field coupling and potential in such a way that the autonomous system converted to a 2D system. Linear stability theory is employed to the extracted critical points to find the nature. From the analysis, we find some interesting cosmological scenarios, such as late-time scalar-field dominated solutions, which evolve in the quintessence era, cannot solve the coincidence problem. Accelerated scaling attractors are also obtained that correspond to the late phase evolution in agreement with present observational data, and these solutions also provide possible mechanisms to alleviate the coincidence problem. A complete cosmic evolution is obtained from early inflation to a late-time dark energy-dominated phase, connecting through a matter-dominated transient phase of the universe. Furthermore, we find that for different values of the interaction parameter α, the evolutionary trajectories of the Hubble parameter, and the distance modulus forecasted by the model are in quite well agreement with observational datasets.