Parametric Resonance versus Forced Oscillation in Time-Evolution of   Quantum Meson Fields
  The time-evolution of quantum meson fields in O(4)-linear sigma model is treated approximately. It is shown that the amplification of the amplitudes of pion modes with low momenta occurs by means of both the parametric resonance and the forced oscillation. 
Y. Tsue (Kochi Univ., Japan)