Nonlinearσmodels for triangular quantum antiferromagnets

We expand the long-wavelength action of two-dimensional quantum Heisenberg antiferromagnets on a triangular lattice around the N\'eel-ordered classical ground state and map it onto a nonlinear model, where the field is an SO (3) element, describing the local orientation of the magnetizations on the three sublattices. No topological information on the microscopic value of the spin S is seen to subsist in the mapping, although some nontrivial third-order terms are found.