Early dark energy and scalarization in a scalar-tensor model

We present a model in which the Gauss-Bonnet invariant holds the quintessence at a fixed point, respecting an initial Z₂ 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 Z₂ symmetry breaking, scalarization occurs, leading to a rapid reduction in the early dark energy density. The model then quickly behaves like the ΛCDM 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.