On the Naturalness of Higgs Inflation

TL;DR

Barbón and Espinosa critically re-evaluate the proposition that the Standard Model Higgs can drive inflation with a large nonminimal coupling to gravity. They show that the underlying effective field theory has a low cutoff set by the Planck scale and the coupling, well below the inflationary plateau energy, and that understanding the inflationary potential requires UV completion beyond this cutoff. The analysis demonstrates that the plateau is highly sensitive to higher-dimension operators and radiative corrections, making the required plateau structure non-generic. Consequently, the naturalness of Higgs inflation with a strong curvature coupling is lost, and the scenario resembles other ad-hoc inflaton potentials that rely on fine-tuning.

Abstract

We critically examine the recent claim that the Standard Model Higgs boson ${\cal H}$ could drive inflation in agreement with observations if $|{\cal H}|^2$ has a strong coupling $ξ\sim 10^4$ 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 $Λ=m_p/ξ$, where $m_p$ is the reduced Planck mass. We then argue that knowing the Higgs potential profile for the field values relevant for inflation ($|{\cal H}|>m_p/\sqrtξ\gg Λ$) 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.