Dynamic structure factor of the three-dimensional Ising model with purely relaxational dynamics.

We compute the dynamic structure factor for the three-dimensional Ising model with a purely relaxational dynamics (model A). We perform a perturbative calculation in the epsilon expansion, at two loops in the high-temperature phase and at one loop in the temperature magnetic-field plane, and a Monte Carlo simulation in the high-temperature phase. We find that the dynamic structure factor is very well approximated by its mean-field Gaussian form up to moderately large values of frequency omega and momentum k. In the region we can investigate, k(xi) less than or equal 5, omega(tau) less than or equal 10, where xi is the correlation length and tau is the zero-momentum autocorrelation time, deviations are at most of a few percent.