The Equation of State of Tracker Fields

TL;DR

This paper derives the equation of state for tracker fields in dark energy models, accounting for late-time deviations, and constrains the model parameter using observational data, finding consistency with a cosmological constant.

Contribution

It provides a new analytical expression for the equation of state of tracker fields considering late-time effects and observational constraints.

Findings

Equation of state depends on $\uOmp$ and a single parameter $w_{(0)}$.

Observational data favor $w_{(0)}$ close to -1.

Results are consistent with a cosmological constant.

Abstract

We derive the equation of state of tracker fields, which are typical examples of freezing quintessence (quintessence with the equation of state approaching toward -1), taking into account of the late-time departure from the tracker solution due to the nonzero density parameter of dark energy $\Omp$. We calculate the equation of state as a function of $\Omp$ for constant $\Gamma=VV"/(V')^2$ (during matter era) models. The derived equation of state contains a single parameter, $w_{(0)}$, which parametrizes the equation of state during the matter-dominated epoch. We derive observational constraints on $w_{(0)}$ and find that observational data are consistent with the cosmological constant: $-1.11< \wzero< -0.96 (1 \sigma)$.