  We show that the mechanism of vortex-antivortex pair production via field
oscillations, earlier proposed by two of us for systems with first order
transitions in presence of explicit symmetry breaking, is in fact very
generally applicable. We further argue that this mechanism applies to all sorts
of topological defects (e.g. strings, monopoles, textures) and for second order
transitions as well. We also show this explicitly by numerically simulating
production of vortex-antivortex pairs by decay of bubble walls for a U(1)
global theory in the absence of any explicit symmetry breaking.
