SPHERICAL SYMMETRICAL SPIN-WAVE THEORY OF HEISENBERG-MODEL

We represent simple decoupling scheme for two-time spin Green's function which leads to the rotational invariant spin wave theory for low dimensional Heisenberg magnetics without broken symmetry and with correct sum rule S ---overnot r2 = S(S+1). For two-dimensional S = 1/2 antiferromagnet this theory predicts disordered ground state while for S > 1/2 it possesses long range order at T = 0. The dynamic structure factor is calculated.