New mechanism to cross the phantom divide

TL;DR

This paper proposes a new scalar field mechanism within modified gravity theories that enables the dark energy equation of state to cross the phantom divide, supported by analytical and numerical solutions across various potentials.

Contribution

It introduces a novel scalar field model in modified gravity that allows crossing the phantom divide, with analytical conditions and numerical validation across multiple potentials.

Findings

The scalar field model enables crossing of the phantom divide.

Analytical solutions demonstrate conditions for crossing.

Numerical results show robustness across different potentials.

Abstract

Recently, type Ia supernovae data appear to support a dark energy whose equation of state $w$ crosses -1, which is a much more amazing problem than the acceleration of the universe. We show that it is possible for the equation of state to cross the phantom divide by a scalar field in the gravity with an additional inverse power-law term of Ricci scalar in the Lagrangian. The necessary and sufficient condition for a universe in which the dark energy can cross the phantom divide is obtained. Some analytical solutions with $w<-1$ or $w>-1$ are obtained. A minimal coupled scalar with different potentials, including quadratic, cubic, quantic, exponential and logarithmic potentials are investigated via numerical methods, respectively. All these potentials lead to the crossing behavior. We show that it is a robust result which is hardly dependent on the concrete form of the potential of the scalar.