Electroweak stability and non-minimal coupling
  The measured values of the Higgs and top quark mass indicate that the
electroweak vacuum is metastable if there is no new physics below the Planck
scale. This is at odds with a period of high scale inflation. A non-minimal
coupling between the Higgs field and the Ricci scalar can stabilize the vacuum
as it generates a large effective Higgs mass during inflation. We consider the
effect of this coupling during preheating, when Higgs modes can be produced
very efficiently due to the oscillating Ricci scalar. We compute their effect
on the effective potential and the energy density. The Higgs excitations are
defined with respect to the adiabatic vacuum. We study the adiabaticity
conditions and find that the dependence of our results on the choice of the
order of the adiabatic vacuum increases with time. For large enough coupling
particle production is so efficient that the Higgs decays to the true vacuum
before this is an issue. However, for smaller values of the Higgs-curvature
coupling no definite statements can be made as the vacuum dependence is large.
