Primordial black holes from spectator field bubbles
  We study the evolution of light spectator fields in an asymmetric polynomial
potential. During inflation, stochastic fluctuations displace the spectator
field from the global minimum of its potential, populating the false vacuum
state and thereby allowing for the formation of false vacuum bubbles. By using
a lattice simulation, we show that these bubbles begin to contract once they
re-enter the horizon and, if sufficiently large, collapse into black holes.
This process generally results in the formation of primordial black holes,
which, due to the specific shape of their mass function, are constrained to
yield at most 1% of the total dark matter abundance. However, the resulting
population can source gravitational wave signals observable at the LIGO-Virgo
experiments, provide seeds for supermassive black holes or cause a transient
matter-dominated phase in the early Universe.
