Critical point Higgs inflation in the Palatini formulation

Abstract

Abstract We study Higgs inflation in the Palatini formulation with the renormalisation group improved potential in the case when loop corrections generate a feature similar to an inflection point. Assuming that there is a threshold correction for the Higgs quartic coupling λ and the top Yukawa coupling yt, we scan the three-dimensional parameter space formed by the two jumps and the non-minimal coupling ξ.The spectral index ns can take any value in the observationally allowed range. The lower limit for the running is αs> −3.5 × 10−3, and αs can be as large as the observational upper limit. Running of the running is small. The tensor-to-scalar ratio is 2.2×10−17< r < 2 × 10−5. We find that slow-roll can be violated near the feature, and a possible period of ultra-slow-roll contributes to the widening of the range of CMB predictions. Nevertheless, for the simplest tree-level action, the Palatini formulation remains distinguishable from the metric formulation even when quantum corrections are taken into account, because of the small tensor-to-scalar ratio.