Out of equilibrium nonperturbative quantum field dynamics in homogeneous external fields

Abstract

The quantum dynamics of the symmetry broken $\ensuremath{\lambda}({\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\Phi}}}^{2}{)}^{2}$ scalar field theory in the presence of an homogeneous external field is investigated in the large N limit. We choose as the initial state the ground state for a constant external field $\mathcal{J}\ensuremath{\rightarrow}.$ The sign of the external field is suddenly flipped from $\mathcal{J}\ensuremath{\rightarrow}$ to $\ensuremath{-}\mathcal{J}\ensuremath{\rightarrow}$ at a given time and the subsequent quantum dynamics calculated. Spinodal instabilities and parametric resonances produce large quantum fluctuations in the field components transverse to the external field. This allows the order parameter to turn around the maximum of the potential for intermediate times. Subsequently, the order parameter starts to oscillate near the global minimum for the external field $\ensuremath{-}\mathcal{J}\ensuremath{\rightarrow},$ entering a novel quasiperiodic regime.