Speaker
Description
Metastability of the Standard Model Higgs during inflation raises the possibility that stochastic fluctuations push the field beyond the instability barrier and into a region of negative energy vacuum. Whether such excursions are fatal to our Universe depends on their fully nonlinear gravitational evolution. We revisit this problem using numerical simulations of a spherically symmetric gravity-scalar-fluid system. We consider an intially radiation dominated Friedmann–Lemaître–Robertson–Walker background with superhorizon fluctuations in the field, which are generated during inflation. We find that once an unstable patch enters classical collapse, it first forms a primordial black hole hiding the crunching true vacuum core within. The late time evolution is controlled by the ratio of the barrier size to its self-gravity $R_w/\ell_\sigma$. For subcritical configurations, the remaining true vacuum region is gradually swallowed by the original black hole. For supercritical configurations, the barrier briefly drives the spacetime into a wormhole-like phase with a second trapped surface and a bifurcating horizon, allowing a transient baby-universe interpretation. In all cases we study, the entire region with field values beyond the potential barrier eventually becomes hidden behind horizons, and the late time exterior is that of an ordinary primordial black hole embedded in an FLRW universe. Our results therefore suggest that field excursions beyond an instability scale are not necessarily catastrophic for the compatibility of inflation with our observed Universe. More broadly, this mechanism is not unique to the Higgs, but is expected to apply quite generally to spectator scalar fields with metastable potentials containing a negative true vacuum.