On UV-completion of Palatini-Higgs inflation

TL;DR

This paper explores UV-completion strategies for Higgs inflation in both metric and Palatini formalisms, finding success in the metric case but persistent low cutoff issues in the Palatini case due to field-space curvature.

Contribution

It introduces a higher-dimensional embedding of the Higgs field-space to address UV-completion, successfully flattening the field-space in the metric formalism but not in the Palatini formalism.

Findings

Successful UV-completion in metric formalism via field-space embedding.

Persistent low cutoff problem in Palatini formalism.

Discussion of conformal symmetry's role in cutoff limitations.

Abstract

We investigate the UV-completion of the Higgs inflation in the metric and the Palatini formalisms. It is known that the cutoff scales for the perturbative unitarity of these inflation models become much smaller than the Planck scale to be consistent with observations. Expecting that the low cutoff scale originates in the curvature of a field-space spanned by the Higgs fields, we consider embedding the curved field-space into a higher dimensional flat space and apply this procedure to the metric-Higgs and the Palatini-Higgs scenarios. The new field introduced in this way successfully flattens the field-space and UV-completes the Higgs inflation in the metric formalism. However, in the Palatini formalism, the new field cannot uplift the cutoff up to the Planck scale. We also discuss the unavoidable low cutoff in the Palatini formalism in the context of the local conformal symmetry.