Successful Higgs inflation from combined nonminimal and derivative couplings

Abstract

We propose an inflationary scenario based on the concurrent presence of nonminimal coupling (NMC) and generalized nonminimal derivative coupling (GNMDC), in the context of Higgs inflation. The combined construction maintains the advantages of the individual scenarios without sharing their disadvantages. In particular, a long inflationary phase can be easily achieved due to the gravitational friction effect owed to the GNMDC, without leading to trans-Planckian values and unitarity violation. Additionally, the tensor-to-scalar ratio remains at low values due to the NMC contribution. Finally, the instabilities related to the squared sound speed of scalar perturbations, which plague the simple GNMDC scenarios, are now healed due to the domination of the NMC contribution and the damping of the GNMDC effects during the reheating era. These features make scenarios with nonminimal and derivative couplings to gravity successful candidates for the description of inflation.