Standard Model with a real singlet scalar and inflation

Abstract

We study the post-inflationary dynamics of the Standard Model Higgs and a real singlet scalar $s$, coupled together through a renormalizable coupling ${\lambda }_{sh}{h}^2{s}^2$, 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 $T_h\sim 10^{14}$ 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.

16 pages, 1 figure, replaced to match published version in JCAP

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