Thermal false vacuum decay near black holes is aspherical

We study decay of a scalar field false vacuum near a (3+1)-dimensional Schwarzschild black hole equilibrated at Hawking temperature with the environment. Our scalar field model has negative quartic self-coupling and thereby resembles Higgs sector of the Standard Model in the large-field limit. We demonstrate that if the black hole is not too small, the false vacuum in this model decays aspherically with regard to the black hole center: via formation of expanding true vacuum bubbles emerging on the outer side of the event horizon. More specifically, we identify three regimes of the decay. For the largest and coldest black holes, the main mechanism is quantum tunneling described by an infinitesimally thin bounce sitting at some point of the horizon. In the intermediate-mass regime, the vacuum is destroyed by thermal fluctuations creating aspherical critical bubbles in the horizon vicinity. Finally, near the smallest black holes thermal fluctuations still guide the decay but the dominant critical bubble is spherically symmetric and covers the entire horizon.