Unitarity and predictiveness in new Higgs inflation

TL;DR

This paper investigates the unitarity and predictiveness of new Higgs inflation, focusing on how unknown UV physics and the non-minimal couplings affect inflationary predictions and their sensitivity to Standard Model parameters.

Contribution

It analyzes the UV dependence of new Higgs inflation and proposes a method to mitigate sensitivity to unknown high-energy physics through non-minimal couplings.

Findings

Inflationary predictions are sensitive to the running of SM parameters.

Non-minimal couplings of fermions and gauge fields can reduce UV sensitivity.

The approach can be applied to other particle physics inflation models.

Abstract

In new Higgs inflation the Higgs kinetic terms are non-minimally coupled to the Einstein tensor, allowing the Higgs field to play the role of the inflaton. The new interaction is non-renormalizable, and the model only describes physics below some cutoff scale. Even if the unknown UV physics does not affect the tree level inflaton potential significantly, it may still enter at loop level and modify the running of the Standard Model (SM) parameters. This is analogous to what happens in the original model for Higgs inflation. A key difference, though, is that in new Higgs inflation the inflationary predictions are sensitive to this running. Thus the boundary conditions at the EW scale as well as the unknown UV completion may leave a signature on the inflationary parameters. However, this dependence can be evaded if the kinetic terms of the SM fermions and gauge fields are non-minimally coupled to gravity as well. Our approach to determine the model's UV dependence and the connection between low and high scale physics can be used in any particle physics model of inflation.