On the naturalness of Higgs inflation

We critically examine the recent claim that the standard model (SM) Higgs boson H could drive inflation in agreement with observations if |H|2 has a strong coupling ξ∼104 to the Ricci curvature scalar. We first show that the effective-theory approach upon which that claim is based ceases to be valid beyond a cutoff scale Λ=mp/ξ, where mp is the reduced Planck mass. We then argue that knowing the Higgs potential profile for the field values relevant for inflation (|H|>mp/ξΛ) requires knowledge of the ultraviolet completion of the SM beyond Λ. In absence of such microscopic theory, the extrapolation of the pure SM potential beyond Λ is unwarranted and the scenario is akin to other ad hoc inflaton potentials afflicted with significant fine-tuning. The appealing naturalness of this minimal proposal is therefore lost. © 2009 The American Physical Society.