Three-particle scattering continuum in quasi-one-dimensional integer-spin Heisenberg magnets

We analyze the three-particle scattering continuum in quasi-one-dimensional integer spin Heisenberg antiferromagnets within a low-energy effective held theory framework. We exactly determine the zero-temperature dynamical structure factor in the O(3) nonlinear sigma model and in Tsvelik's Majorana fermion theory. We study the effects of interchain coupling in a random phase approximation. We discuss the application of our results to recent neutron-scattering experiments on the spin-1 Haldane-gap material CsNiCl3.