KINETICS OF SYSTEMS WITH CONTINUOUS SYMMETRY UNDER THE EFFECT OF AN EXTERNAL-FIELD

Universality in the kinetics of systems with O(N) continuous symmetry, under influence of an external time-dependent field, is studied. The exponents that characterize the process are obtained, showing that the y are independent of N, for N greater-than-or-equal-to 2. We also get analytical expressions for the time dependence of the order parameter (magnetization) in the presence of small fields, in the limit N --> in finity. Our results show that universality goes beyond the value of th e exponents. For small fields, the full dynamical evolution of the ord er parameter is universal. Similar universality is expected for arbitr ary N. Agreement with numerical solutions of the basic nonlinear equat ions is excellent.