Massless preheating and electroweak vacuum metastability

Current measurements of Standard Model parameters suggest that the electroweak vacuum is metastable. This metastability has important cosmological implications, because large fluctuations in Higgs field could trigger decay early Universe. For false to survive, interactions which stabilize during inflation---e.g., inflaton-Higgs or nonminimal couplings gravity---are typically necessary. However, postinflationary preheating dynamics these same also decay, thereby recreating problem we sought avoid. often assumed catastrophic for models exhibiting scale invariance, since generically allow unimpeded growth fluctuations. In this paper, examine such ``massless preheating'' scenarios and show competing threats can nonetheless be balanced ensure viability. We find fully accounting both backreaction from particle production effects perturbative decays reveals a number disjoint ``islands (meta)stability'' over parameter space couplings. Ultimately, interplay among Higgs-stabilizing plays significant role, leading sequence dynamical phases effectively extend metastable regions Higgs-curvature