The Decay of the Standard Model Higgs after Inflation

TL;DR

This study uses lattice simulations to analyze how the Standard Model Higgs decays after inflation, revealing rapid decay into gauge bosons and eventual thermalization, with a derived formula for decay time based on key parameters.

Contribution

First detailed nonperturbative simulation of Higgs decay dynamics post-inflation in the Standard Model framework.

Findings

Higgs decays rapidly into Z and W bosons after inflation.

Energy distribution among species reaches equipartition before thermalization.

Derived a master formula for Higgs decay time based on simulation parameters.

Abstract

We study the nonperturbative dynamics of the Standard Model (SM) after inflation, in the regime where the SM is decoupled from (or weakly coupled to) the inflationary sector. We use classical lattice simulations in an expanding box in (3+1) dimensions, modeling the SM gauge interactions with both global and Abelian-Higgs analogue scenarios. We consider different post-inflationary expansion rates. During inflation, the Higgs forms a condensate, which starts oscillating soon after inflation ends. Via nonperturbative effects, the oscillations lead to a fast decay of the Higgs into the SM species, transferring most of the energy into $Z$ and $W^{\pm}$ bosons. All species are initially excited far away from equilibrium, but their interactions lead them into a stationary stage, with exact equipartition among the different energy components. From there on the system eventually reaches equilibrium. We have characterized in detail, in the different expansion histories considered, the evolution of the Higgs and of its dominant decay products, until equipartition is established. We provide a useful mapping between simulations with different parameters, from where we derive a master formula for the Higgs decay time, as a function of the coupling constants, Higgs initial amplitude and postinflationary expansion rate.