Predictions on mass of Higgs portal scalar dark matter from Higgs inflation and flat potential

We consider the Higgs portal Z2 scalar model as the minimal extension of the Standard Model (SM) to incorporate the dark matter. We analyze this model by using the two-loop renormalization group equations. We find that the dark matter mass is bounded to be lighter than 1000 GeV within the framework that we have proposed earlier, where the Higgs inflation occurs above the SM cutoff Λ, thanks to the fact that the Higgs potential becomes much smaller than its typical value in the SM: V ≪ Λ4. We can further fix the dark matter mass to be 400 GeV < mDM< 470 GeV if we impose that the cutoff is at the string scale Λ ~ 1017 GeV and that the Higgs potential becomes flat around Λ, as is required by the multiple point principle or by the Higgs inflation at the critical point. This prediction is testable by the dark matter detection experiments in the near future. In this framework, the dark matter and top quark masses are strongly correlated, which is also testable.