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

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