Standard Model with a real singlet scalar and inflation

We study the post-inflationary dynamics of the Standard Model Higgs and a real singlet scalar s , coupled together through a renormalizable coupling λ sh h 2 s 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 ∼ 10 14 GeV, whereas s thermalizes typically around T s ∼ 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 λ sh ≲ 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.