Higgs ξ-inflation for the 125-126 GeV Higgs: a two-loop analysis

A non-minimal coupling xi of the Standard Model Higgs field to gravity can give rise to inflation, but large xi is required and thus leads to a violation of perturbative unitarity at M-P1/xi, which is well below the inflationary scale M-P1/root xi. We re-examine this claim for a Higgs mass in the range 125-126 GeV for which lambda(eff)(mu) runs to very small values near the Planck scale and can significantly reduce the value of xi required for inflation. Using the two-loop renormalization group equations and effective potential for Higgs xi-inflation, we find that familiar inflationary solutions can have a non-minimal coupling as small as xi similar to 400 without the potential developing a second minimum. We also find a new observationally allowed region of Higgs xi-inflation with xi similar to 90 and distinct inflationary predictions, including an observable level of the tensor-to-scalar ratio r.