Is Higgs inflation ruled out?

Abstract

We consider the status of Higgs inflation in light of the recently announced detection of B modes in the polarization of the cosmic microwave background radiation by the BICEP2 Collaboration. In order for the primordial B-mode signal to be observable by BICEP2, the energy scale of inflation must be high: Vinf≈2×1016-GeV. Higgs inflation generally predicts a small amplitude of tensor perturbations, and therefore it is natural to ask if Higgs inflation might accommodate this new measurement. We find that the answer is essentially no, unless one considers either extreme fine-tuning or possibly adding new beyond the Standard Model fields, which remove some of the more attractive features of the original idea. We also explore the possible importance of a factor that has not previously been explicitly incorporated, namely the gauge dependence of the effective potential used in calculating inflationary observables (e.g., nS and r), to see if this might provide additional wiggle room. Such gauge effects are comparable to the effects of Higgs mass uncertainties and other observables already considered in the analysis, and therefore they are relevant for constraining models. However, they are therefore too small to remove the apparent incompatibility between the BICEP2 observation and the predictions of Higgs inflation.