Higgs inflation at the critical point

Higgs inflation can occur if the Standard Model (SM) is a self-consistent effective field theory up to inflationary scale. This leads to an upper bound on the top Yukawa coupling, ytphys<ytcrit and thus on the mass of the top quark mt. If mt is more than a few hundred of MeV below the critical value, the Higgs inflation predicts the universal values of inflationary indexes, r≃0.003 and ns≃0.97, independently on the SM parameters. We show that in the vicinity of the critical point ytcrit the inflationary indexes acquire an essential dependence on mt and on the mass of the Higgs boson Mh. In particular, the amplitude of the gravitational waves can exceed considerably the universal value.