Parametrization of Dark Energy Equation of State

TL;DR

This paper compares different models of dark energy's equation of state, evaluating their physical viability and compatibility with cosmological observations, especially focusing on the Hannestad parametrization and its limitations.

Contribution

It provides a comprehensive comparison of dark energy parametrizations and critically assesses the Hannestad model's strengths and weaknesses in cosmological contexts.

Findings

Hannestad parametrization is simple and transparent for dark energy evolution.

It fails to satisfy BBN constraints with best-fit parameters.

Extended parameter space shows better compatibility with observations.

Abstract

A comparative study of various parametrizations of the dark energy equation of state $w(z)$ and its variation with the redshift is made. Astrophysical constraints from 'integrated tracking' are laid down to test the physical viability and cosmological compatibility of these parametrizations. A critical evaluation of the 4-index Hannestad parametrization is done. It is found to be simple and transparent in probing the evolution of the dark energy during the expansion history of the universe but it does not satisfy the BBN constraint on the dark energy density parameter for the best fit values; however it looks more compatible with the observations in the extended parameter space with $w<< -1$.