Standard Model with a real singlet scalar and inflation

TL;DR

This paper investigates the post-inflationary evolution of the Higgs and a singlet scalar in a $Z_2$ symmetric model, analyzing their thermalization, decay, and potential to account for dark matter and baryon asymmetry.

Contribution

It provides a detailed analysis of the thermalization and decay processes of Higgs and singlet condensates after inflation, highlighting the impact of thermal effects and large background fields.

Findings

Higgs condensate thermalizes around 10^{14} GeV

Singlet scalar thermalizes around 10^{6} GeV

Possible dark matter production via condensate fragmentation

Abstract

We study the post-inflationary dynamics of the Standard Model Higgs and a real singlet scalar $s$, coupled together through a renormalizable coupling $\lambda_{sh}h^2s^2$, in a $Z_2$ symmetric model that may explain the observed dark matter abundance and/or the origin of baryon asymmetry. The initial values for the Higgs and $s$ condensates are given by inflationary fluctuations, and we follow their dissipation and relaxation to the low energy vacua. We find that both the lowest order perturbative and the non-perturbative decays are blocked by thermal effects and large background fields and that the condensates decay by two-loop thermal effects. Assuming instant reheating at $T=10^{16}$ GeV, the characteristic temperature for the Higgs condensate thermalization is found to be $T_h \sim 10^{14}$ GeV, whereas $s$ thermalizes typically around $T_s \sim 10^{6}$ GeV. By that time, the amplitude of the singlet is driven very close to the vacuum value by the expansion of the universe, unless the portal coupling takes a value $\lambda_{sh}\lesssim 10^{-7}$ and the singlet $s$ never thermalizes. With these values of the coupling, it is possible to slowly produce a sizeable fraction of the observed dark matter abundance via singlet condensate fragmentation and thermal Higgs scattering. Physics also below the electroweak scale can therefore be affected by the non-vacuum initial conditions generated by inflation.