Phenomenological Dark Energy model with hybrid dynamic Cosmological Constant

We investigate Dark Energy by associating it with vacuum energy or Cosmological constant Λ which is taken to be dynamic in nature. Our approach is phenomenological and falls within the domain of variable-Λ Cosmology. However, motivated by quantum theory of metastable vacuum decay, we proposed a new phenomenological decay law of Λ(t) where Λ(t) is a superposition of constant and variable components viz. Λ(t) = ΛC + Λv which is indicated by the word “hybrid dynamic” in the title. By taking a simplified two-fluid scenario with the Universe consisting of Dark Energy and another major component, we found the solutions for three particular phenomenological expressions and made a parametrization of the model in terms of dilution parameter (u). For pressureless Dust and dynamic Dark Energy Universe, we found the matter density and dilution parameter (the dilution parameter has been defined in the text as the exponent of scale factor in the expression of density of the other major component, representing the dilution of the component with the expansion of Universe in the presence of dynamic Dark Energy) to be Ωm0 = 0.29 ± 0.03, u = 2.90 ± 0.54 at 1σ by analysing 580 supernova from Union 2.1 catalogue. The physical features of the model in regard to scale factor evolution, deceleration parameter, cosmic age has also been studied and parallels have been drawn with ΛCDM model. The status of Cosmological problems in the model has also been checked which showed that the model solves the Cosmological Constant Problem but the Coincidence problem still exists in the model.

Transit cosmological models in FRW universe under the two-fluid scenario

This paper is an attempt to revisit the Friedmann–Robertson–Walker (FRW) cosmological models under the new scenario of observational cosmology, which has established that the current universe is expanding with an increasing rate, in contrast to the earlier belief that the rate of expansion is constant or slowing down. This paper represents a model which encompasses both, earlier decelerating and the current accelerating universe, passing through a transition phase. The universe is assumed to be filled with two fluids, barotropic and dark energy. We have considered two cases; first, when these fluids are assumed to be non-interacting and second, when they interact with each other. Some physical, kinematic and geometric properties of the model are also discussed along with the acceptability and stability of the solution. The results found are very compatible with the established results as well as recent observations.

An interacting two-fluid scenario for dark energy in anisotropic cosmological model

The open anisotropic cosmological model of the early Universe is considered. We study the evolution of the dark energy parameter within anisotropic Bianchi type-V cosmological model filled with barotropic fluid and dark energy. The solutions have been obtained for power law and exponential forms of the expansion parameter. (They correspond to constant deceleration parameter in general relativity.) For large time (i.e., t → ∞), the models tend asymptotically to an isotropic Friedmann–Robertson–Walker cosmological model under certain conditions.