A COUPLED-CLUSTER FORMULATION OF HAMILTONIAN LATTICE FIELD-THEORY - THE NONLINEAR SIGMA-MODEL

We apply the coupled cluster method (CCM) to the Hamiltonian version o f the latticised O(4) nonlinear sigma model. The method, which was ini tially developed for the accurate description of quantum many-body sys tems, gives rise to two distinct approximation schemes. These approach es are compared with each other as well as with some other Hamiltonian approaches. Our study of both the ground state and collective excitat ions leads to indications of a possible chiral phase transition as the lattice spacing is varied. (C) 1998 Academic Press.