Hubble-induced phase transitions and Higgs dynamics in the early Universe

A non-minimal coupling between scalar fields and spacetime curvature can play a central role in the history of the early Universe. For a prototypical spectator field, the time dependence of the Ricci scalar acts as a cosmic clock that can trigger a second-order phase transition as the Universe evolves from inflation to kination. In this talk, I will show how such Hubble-induced phase transitions can efficiently reheat the Universe through non-perturbative particle production, while simultaneously sourcing a stochastic gravitational-wave background. The non-linear dynamics of this process is captured using classical lattice simulations, allowing for a systematic exploration of the model’s parameter space. Focusing on the case of the non-minimally coupled Higgs, I will discuss how electroweak vacuum stability constrains the viable parameter space of the model. When these constraints are satisfied, the Higgs can drive efficient reheating into a Standard Model plasma prior to big bang nucleosynthesis. The associated gravitational-wave signal offers a window into the high-energy features of the Higgs effective potential.