Abstract
The approximate mapping of the antiferromagnetic Heisenberg chain onto a (1+1)-dimensional quantum field theory indicates that the ground state is disordered with a finite gap for integer spin. We study a lattice of coupled (1+1)-dimensional field theories as a model for weakly coupled spin chains. This model offers a possible resolution to the mystery of the upper mode in the low-temperature ordered phase of CsNiCl3, whose polarization is inconsistent with spin-wave theory.