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 vertical bar H vertical bar(2) has a strong coupling xi similar to 10(4) 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 Lambda=m(p)/xi, where m(p) is the reduced Planck mass. We then argue that knowing the Higgs potential profile for the field values relevant for inflation (vertical bar H vertical bar > m(p)/root xi root >Lambda) requires knowledge of the ultraviolet completion of the SM beyond Lambda. In absence of such microscopic theory, the extrapolation of the pure SM potential beyond Lambda 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.