Field theoretical approach to spin models

We developed a systematic non-perturbative method base on Dyson-Schwinger theory and the derivable for Ising model at broken phase. Based these methods, we obtain critical temperature spin correlation beyond mean field theory. The spectrum of Green function obtained from our methods become gapless point, so susceptibility divergent Tc. this is fairly good in comparison with other non-cluster methods. It straightforward to extend more complicate models example continue symmetry.