Phenomenological dark energy model with hybrid dynamic cosmological constant

Abstract

We investigate dark energy (DE) 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 DE 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 (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 DE). For pressureless dust and dynamic DE Universe, we found the present day matter density (Ω m0) and dilution parameter (u) to be Ω m0 = 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.