Kinetics of phase ordering in the O(n) model with a conserved order parameter

We study the phase-ordering dynamics of the O(n) model with a conserved ord er parameter for systems with topological defects. We present results from both cell dynamical simulations and predictions of a Gaussian auxiliary fie ld (GAF) approximation for the XY (n = 2) model in two and three dimensions , and the Heisenberg (n = 3) model in three dimensions. We describe the res ults for the structure factor S(q) and growth law L(t) from simulations. Th e growth laws obtained are consistent with theoretical predictions based on energy-scaling arguments. The structure factor shows good dynamical scalin g using a length extracted from its first moment. The simulations are compa red with the theoretical predictions of the GAF for the scaling functions. Our results show that the GAF gives a good qualitative description of most features of the structure factor. However, it overestimates the amplitude o f the Pored tail in the large-q limit. Moreover, for small q, the structure factor exhibits a q(2)-behaviour instead of the expected (generalized) Yeu ng result of q(4).