The zero-curvature representation for nonlinear O(3) sigma-model
arXiv:hep-th/9403101
Abstract
We consider O(3) sigma-model as a reduction of the principal chiral field. This approach allows to introduce the currents with ultralocal Poisson brackets and to obtain the zero-curvature equation which admits the fundamental Poisson bracket.
Uppsala University preprint, 12 pages, LaTeX file