Goldstone-mode effects and scaling function for the three-dimensional O(4)model

We investigate numerically the three-dimensional O(4) model on 24(3)-120(3) lattices as a function of the magnetic field H. We verify explicitly the s ingularities induced by Goldstone modes in the low-temperature phase of the model, and show that they are also observed close to the critical temperat ure. Our results are well described by the perturbative form of the model's magnetic equation of state, with coefficients determined nonperturbatively from our data. The resulting expression Is used to generate the magnetizat ion's scaling function parametrically. (C) 2000 Elsevier Science B.V. All r ights reserved.