  We develop an approach to investigate the non-perturbative dynamics of
quantum field theories, in which specific vacuum field fluctuations are treated
as the low-energy dynamical degrees of freedom, while all other vacuum field
configurations are explicitly integrated out from the path integral. We show
how to compute the effective interaction between the vacuum field degrees of
freedom both perturbatively (using stochastic perturbation theory) and fully
non-perturbatively (using lattice field theory simulations). The present
approach holds to all orders in the couplings and does not rely on the
semi-classical approximation.
