Higgs field-curvature coupling and postinflationary vacuum instability

We study the postinflationary dynamics of the Standard Model (SM) Higgs field in the presence of a nonminimal coupling xi|Phi|R-2 to gravity, both with and without the electroweak gauge fields coupled to the Higgs field. We assume a minimal scenario in which inflation and reheating are caused by chaotic inflation with a quadratic potential, and no additional new physics is relevant below the Planck scale. By using classical real-time lattice simulations with a renormalization group improved effective Higgs potential and by demanding the stability of the Higgs vacuum after inflation, we obtain upper bounds for xi taking into account the experimental uncertainty of the top-Yukawa coupling. We compare the bounds in the absence and presence of the electroweak gauge bosons and conclude that the addition of gauge interactions has a rather minimal impact. In the unstable cases, we parametrize the time when such instability develops. For a top-quark mass m(t) approximate to 173.3 GeV, the Higgs vacuum instability is triggered for xi greater than or similar to 4-5, although a slightly lower mass of m(t) approximate to 172.1 GeV pushes up this limit to xi greater than or similar to 11-12. This, together with the estimation xi greater than or similar to 0.06 for stability during inflation, provides tight constraints to the Higgs field-curvature coupling within the SM.