  We investigate false vacuum decay of a relativistic scalar field initialized
in the metastable minimum of an asymmetric double-well potential. The
transition to the true ground state is a well-defined initial-value problem in
real time, which can be formulated in nonequilibrium quantum field theory on a
closed time path. We employ the non-perturbative framework of the two-particle
irreducible (2PI) quantum effective action at next-to-leading order in a
large-N expansion. We also compare to classical-statistical field theory
simulations on a lattice in the high-temperature regime. By this, we
demonstrate that the real-time decay rates are comparable to those obtained
from the conventional Euclidean (bounce) approach. In general, we find that the
decay rates are time dependent. For a more comprehensive description of the
dynamics, we extract a time-dependent effective potential, which becomes convex
during the nonequilibrium transition process. By solving the quantum evolution
equations for the one- and two-point correlation functions for vacuum initial
conditions, we demonstrate that quantum corrections can lead to transitions
that are not captured by classical-statistical approximations.
