  Considering a variety of dynamical scenarios within the linear sigma model,
we examine the conditions for pionic modes to be amplified as the chiral field
relaxes towards the normal vacuum following the transient restoration of
approximate chiral symmetry in a high-energy collision. While Bjorken-type
longitudinal expansions appear to be insufficient for amplification for occur,
analoguos expansions in two or three dimensions may enhance the low-energy
power spectrum by up to an order of magnitude.
