Cosmology after Phantom Crossing by Horndeski Gravity

TL;DR

This paper explores how shift symmetric Horndeski gravity models can explain the crossing of the dark energy equation of state over the phantom divide, emphasizing the impact on cosmic structure growth and lensing.

Contribution

It identifies three main pathways within shift symmetric Horndeski gravity that allow for phantom crossing, analyzing their implications for cosmic expansion and structure formation.

Findings

Multiple models can realize phantom crossing with distinct kinetic structures.

Implications for growth of large-scale structure and lensing are discussed.

The behavior of the equation of state after crossing is characterized.

Abstract

One possible way to explain the observed effective dark energy equation of state crossing $w=-1$ (the phantom divide) is through modified gravity. A key point is to not view the expansion history in isolation but to take into account the other gravitational impacts on growth of large scale structure, lensing, etc. Within shift symmetric Horndeski gravity this implies three main paths for the late time cosmic expansion. All require unusual kinetic structure and we analyze their various implications for how $w$ should behave after phantom crossing.