Early dark energy and scalarization in a scalar-tensor model

TL;DR

This paper proposes a scalar-tensor model where early dark energy, driven by the Gauss-Bonnet invariant, is initially significant but rapidly diminishes due to scalarization, aligning with observational constraints and resembling the DM model.

Contribution

It introduces a novel scalar-tensor framework with Z2 symmetry breaking that explains early dark energy dynamics and its transition to DM-like behavior.

Findings

Early dark energy becomes significant around matter-radiation equality.

Scalarization causes rapid reduction of early dark energy density.

Model aligns with gravitational wave speed constraints.

Abstract

We present a model in which the Gauss-Bonnet invariant holds the quintessence at a fixed point, respecting an initial $Z_2$ symmetry in the radiation-dominated era. This results in an early dark energy that becomes significant around the matter-radiation equality era. However, due to $Z_2$ symmetry breaking, scalarization occurs, leading to a rapid reduction in the early dark energy density. The model then quickly behaves like the $\Lambda$CDM model. This scenario may also explain the reduction of sound horizon and aligns with the assumption that the gravitational wave speed is infinitesimally close to the speed of light.