Transient dark energy, cosmological constant boundary crossing and dark energy $w(z)$ data fits

TL;DR

This paper introduces a dark energy model with a variable speed of sound that allows crossing the cosmological constant boundary and can behave as a transient phenomenon, matching recent observational data fits.

Contribution

It develops an analytical formalism for dark energy with a speed of sound dependent on the equation of state, enabling detailed study of boundary crossing and transient behavior.

Findings

Model reproduces features of recent $w(z)$ observational fits

Demonstrates dark energy can be transient in specific regimes

Provides analytical solutions for dark energy dynamics

Abstract

The formalism of dark energy based on modeling speed of sound as a function of equation of state parameter is elaborated. A specific model which allows detailed study of cosmological constant boundary crossing is introduced and analytical solutions for the model dynamics are obtained. It is shown how in specific parameter regimes dark energy can be a transient phenomenon. It is further demonstrated how the model reproduces specific features of recent fits of dark energy $w(z)$ to observational data.