Gauge singlet scalar as inflaton and thermal relic dark matter

Abstract

We show that, by adding a gauge singlet scalar $S$ to the standard model which is nonminimally coupled to gravity, $S$ can act both as the inflaton and as thermal relic dark matter. We obtain the allowed region of the $({m}_{s},{m}_{h})$ parameter space which gives a spectral index in agreement with observational bounds and also produces the observed dark matter density while not violating vacuum stability or nonperturbativity constraints. We show that, in contrast to the case of Higgs inflation, once quantum corrections are included the spectral index is significantly larger than the classical value ($n=0.966$ for $N=60$) for all allowed values of the Higgs mass ${m}_{h}$. The range of Higgs mass compatible with the constraints is $145\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}170\text{ }\text{ }\mathrm{GeV}$. The $S$ mass lies in the range $45\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{s}\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{TeV}$ for the case of a real $S$ scalar with large quartic self-coupling ${\ensuremath{\lambda}}_{s}$, with a smaller upper bound for smaller ${\ensuremath{\lambda}}_{s}$. A region of the parameter space is accessible to direct searches at the LHC via $h\ensuremath{\rightarrow}SS$, while future direct dark matter searches should be able to significantly constrain the model.