On the Naturalness of Higgs inflation

We critically examine the recent claim that the Standard Model Higgs boson H could drive inflation in agreement with observations if |H | 2 has a strong coupling ξ ∼ 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 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 / √ ξ ≫ Λ) 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. 1 The Standard Model Higgs as the Inflaton Following 1 let us consider the SM Higgs sector corrected by a curvature-induced mass term for the Higgs boson: