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 ½, 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 $\frac{1}{2Sz}$, where $z$ is the number of nearest neighbors. For large $S$ the $\frac{1}{S}$ factor presumably provides convergence, as assumed by Oguchi, whereas for $S=\frac{1}{2}$ the expansion parameter reduces to $\frac{1}{z}$, as discussed in the preceding paper.