Hubble-induced phase transitions on the lattice with applications to Ricci reheating

TL;DR

This study uses lattice simulations to analyze how a spectator field non-minimally coupled to gravity undergoes phase transitions after inflation, revealing universal behaviors that facilitate radiation domination and impact early universe cosmology.

Contribution

It demonstrates that gradient energy becomes significant after phase transitions, leading to universal equation-of-state behavior and enabling radiation domination with various potentials.

Findings

Gradient energy density grows to match kinetic energy.

Equation-of-state approaches 1/3 universally.

Spectrum at transition is non-thermal.

Abstract

Using 3+1 classical lattice simulations, we follow the symmetry breaking pattern and subsequent non-linear evolution of a spectator field non-minimally coupled to gravity when the post-inflationary dynamics is given in terms of a stiff equation-of-state parameter. We find that the gradient energy density immediately after the transition represents a non-negligible fraction of the total energy budget, steadily growing to equal the kinetic counterpart. This behaviour is reflected on the evolution of the associated equation-of-state parameter, which approaches a universal value $1/3$, independently of the shape of non-linear interactions. Combined with kination, this observation allows for the generic onset of radiation domination for arbitrary self-interacting potentials, significantly extending previous results in the literature. The produced spectrum at that time is, however, non-thermal, precluding the naive extraction of thermodynamical quantities like temperature. Potential identifications of the spectator field with the Standard Model Higgs are also discussed.