Phenomenological Dark Energy model with hybrid dynamic Cosmological Constant

TL;DR

This paper proposes a phenomenological model of dark energy with a hybrid dynamic cosmological constant, analyzing its implications on cosmic evolution and fitting it to supernova data, addressing the cosmological constant problem.

Contribution

It introduces a new decay law for the cosmological constant combining constant and variable parts, and explores its effects on cosmic parameters and problems.

Findings

Model fits supernova data with $\

Model solves the Cosmological Constant Problem but not the Coincidence problem.

Provides solutions for scale factor evolution, deceleration parameter, and cosmic age.

Abstract

We investigate Dark Energy by associating it with vacuum energy or Cosmological constant ${\Lambda}$ which is taken to be dynamic in nature. Our approach is phenomenological and falls within the domain of variable-$\Lambda$ Cosmology. However, motivated by quantum theory of metastable vacuum decay, we proposed a new phenomenological decay law of $\Lambda$(t) where $\Lambda$(t) is a superposition of constant and variable components viz. $\Lambda$(t) = $\Lambda_{C}$ + $\Lambda_{v}$ 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 (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). For pressureless Dust and dynamic Dark Energy Universe, we found the present-day matter density ($\Omega_{m0}$) and dilution parameter (u) to be $\Omega_{m0}$ = 0.29 $\pm$ 0.03, u = 2.90 $\pm$ 0.54 at 1 $\sigma$ 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 $\Lambda$CDM 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.