Phantom Dark Energy Models with a Nearly Flat Potential

TL;DR

This paper shows that phantom dark energy models with nearly flat potentials converge to a universal behavior for the equation of state parameter w(a), matching quintessence models, and can be well approximated by a linear parametrization at low redshifts.

Contribution

It demonstrates the convergence of phantom dark energy models to a universal w(a) form under slow roll conditions, aligning their behavior with quintessence models.

Findings

All such phantom models converge to a single w(a) expression.

The universal w(a) matches that of quintessence models in the same limit.

At z<1, w(a) is well fit by a linear parametrization w=w_0 + w_a(1-a).

Abstract

We examine phantom dark energy models produced by a field with a negative kinetic term and a potential that satisfies the slow roll conditions: [(1/V)(dV/dphi)]^2 << 1 and (1/V)(d^2 V/dphi^2) << 1. Such models provide a natural mechanism to produce an equation of state parameter, w, slightly less than -1 at present. Using techniques previously applied to quintessence, we show that in this limit, all such phantom models converge to a single expression for w(a), which is a function only of the present-day values of Omega_phi and w. This expression is identical to the corresponding behavior of w(a) for quintessence models in the same limit. At redshifts z < 1, this limiting behavior is well fit by the linear parametrization, w=w_0 + w_a(1-a), with w_a \approx -1.5(1+w_0).