International Journal of Science and Technology (IJST)

A Study of Time Dependence of Cosmological Parameters for a Dynamical Cosmological Constant Using a Hybrid Scale Factor

In the present study we have determined the time dependence of some cosmological parameters of an isotropic and homogeneous universe, based on an empirical scale factor. The scale factor has been chosen in a manner such that the deceleration parameter changes sign from positive to negative as time goes on. This behaviour of the scale factor is consistent with the transition of the state of the universe from a decelerated expansion to its present state of accelerated expansion. This empirical scale factor is a product of exponential and power-law functions of time, which is often referred to as the hybrid scale factor. First part of the study is based on a constant equation of state (EoS) parameter and its second part is based on a time-varying EoS parameter. The gravitational constant is shown by this model to be decreasing with time. The cosmological constant (denoted by lambda), is found in the present study to be increasing with time, with a gradually decreasing rate of change. In the early universe it rises very steeply from a negative value to a less negative value at the present time, and then, as per predictions by this model, it is likely to increase very slowly to reach a positive value in future. All our theoretical findings have been depicted here graphically.