SCALING SOLUTION FOR COSMOLOGICAL SIGMA-MODELS AT LARGE-N

We study the evolution of the nonlinear O(N) sigma-model in an expanding universe in the large-N approximation, where one can solve exactly for the scaling field distribution, incorporating the full nonlinear dynamics. This provides a valuable analytic approximation for theories of cosmic global monopoles (N = 3), global texture (N = 4), and "nontopological texture" (N > 4). The analytic results are compared with those from numerical simulations, with good agreement. The probability distribution for mass fluctuations in the linear regime is positively skewed, providing a distinctive test for the theory.