Non-canonical Higgs inflation

Abstract

The large value of non-minimal coupling constant ξ required to satisfy cosmic microwave background observations in Higgs inflation violates unitarity. In this work we study Higgs-inflation with non-canonical kinetic term of DBI form to find whether ξ can be reduced. To study the inflationary dynamics, we transform the action to the Einstein frame, in which the Higgs is minimally coupled to gravity with a non-canonical kinetic term and modified potential. We choose the Higgs self coupling constant λ = 0.14 for our analysis. We find that the value of ξ can be reduced from 103–104 to O(10) to satisfy Planck constraints on amplitude of scalar power spectrum. However, this model produces a larger tensor-to-scalar ratio r, in comparison to the Higgs inflation with canonical kinetic term. We also find that, to satisfy joint constraints on scalar spectral index ns and tensor-to-scalar ratio r from Planck-2018 and bounds on r from Planck and BICEP3, the value of ξ should be of the order of 104. Thus, the issue of unitarity violation remains even after considering Higgs inflation with non-canonical kinetic term.