A new extended quintessence

TL;DR

This paper introduces a novel form of extended quintessence dark energy by coupling a scalar field to the Ricci scalar via the Palatini formalism, allowing the equation of state to cross the phantom divide and oscillate.

Contribution

It proposes a new extended quintessence model using Palatini formalism, enabling unique dynamical behaviors of dark energy not seen in previous models.

Findings

Equation of state crosses the phantom divide line.

The equation of state oscillates around -1.

The universe evolves into a de Sitter phase.

Abstract

Extended quintessence is obtained by coupling a normal scalar field to the Ricci scalar defined in the metric formalism. In this paper, we propose a new extended quintessence dark energy by introducing a non-minimal coupling between the quintessence and gravity, but with the Ricci scalar given from the Palatini formalism rather than the metric one. We find that the equation of state of the new extended quintessence can cross the phantom divide line, and moreover, it oscillates around the -1 line. We also show that the universe driven by the new extended quintessence will enter a dark energy dominated de Sitter phase in the future.