Wick and Goldstone Theorems for General Spin; Antiferromagnetic Spin Waves. II

The analogs of Wick's theorem and of Goldstone's theorem, proved in a previous paper for spin {}, are generalized to arbitrary spin. The proof is based on the Schwinger coupled-boson representation of spin operators. Quantum corrections to the spin-wave modes in antiferromagnets are again considered, and it is shown that these corrections can be expanded in powers of 1/2Sz, where z is the number of nearest neighbors. For large S the 1/S factor presumably provides convergence, as assumed by Oguchi, whereas for S=1/2 the expansion parameter reduces to 1/z, as discussed in the preceding paper.