Effect of interchain coupling on spin correlation functions of spin-1 Heisenberg antiferromagnet CsNiCl3

The inelastic neutron-scattering experiment on CsNiCl3 gives much bigger total intensity of multi-particle continuum than the theoretical calculation by the (1+11+1)-dimensional O(3) non-linear σ-model. Three-dimensional effect has to be considered. A scenario was proposed where the interchain interaction is treated as an effective staggered magnetic field. We propose another model to approximately include the effect of the interchain coupling, and use the large-N expansion to do the calculations. In this circumstance we find that the Néel temperature is about 5 K, and also that for a range of wave-vectors the single magnon is unstable and will decay into three magnons.