FINITE-SIZE EFFECTS, GOLDSTONE BOSONS AND CRITICAL EXPONENTS IN THE D=3 HEISENBERG-MODEL

The d = 3 classical O(3) Heisenberg model is studied numerically in the broken phase close to the critical point. The finite-size behaviour of the magnetisation and the correlation functions are shown to be in excellent agreement with the theoretical predictions obtained by chiral perturbation theory. The finite-size effects are governed by two constants, which are defined at infinite volume and zero magnetic field: the Goldstone boson decay constant F (or helicity modulus-UPSILON = F2) and the magnetisation-SIGMA. The data determine the scaling behaviour of SIGMA and F leading to the prediction 0.6930(2) for the critical coupling on simple cubic lattices and nu' = 0.73(4) and beta = 0.36(2) for the correlation length and magnetisation critical indices, respectively.