Primordial black holes and scalar induced gravitational waves from Higgs inflation with noncanonical kinetic term

We resolve the potential-restriction problem in K/G inflation by introducing nonminimal coupling. In this context, Higgs field successfully drives inflation satisfying cosmic microwave background (CMB) observations while enhancing curvature perturbations at small scales, which in turn accounts for primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). We then uncover the effect of the noncanonical kinetic coupling function in more detail and study its the observational constraint. Besides, we also give the gauge invariant expression for the integral kernel of SIGWs, which is related to terms propagating with the speed of light. Finally, the non-Gaussian effect on PBH abundance and SIGWs is studied. We find that non-Gaussianity makes PBHs form more easily, but its effect on the energy density of SIGWs is negligible.