Higgs inflation and general initial conditions

A Higgs field of particle physics can play the role of the inflaton in the early universe if it is non-minimally coupled to gravity. The Higgs inflation scenario predicts a small tensor to scalar ratio: r ≅ 0.003. Although this value is consistent with the upper bound r < 0.12 given by the BICEP2/Keck Array and Planck data, it is not at their maximum likelihood point: r ≅ 0.05. Inflationary observables depend not only on the inflationary models, but they also depend on the initial conditions of inflation. Changing the initial state of inflation can improve the value of r. In this work, we study the Higgs inflation model under general initial conditions and show that there is a subset of these general initial conditions which leads to enhancement of r. Then we show that this region of parameter space is consistent with a non-Gaussianity bound. (orig.)