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

中文翻译：

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自旋模型的场理论方法

我们基于 Dyson-Schwinger 理论和 Ising 模型的可推导理论开发了一种系统的非微扰方法。基于这些方法，我们获得了超出平均场理论的临界温度和自旋自旋相关性。从我们的方法中获得的格林函数谱在临界点变得无间隙，因此敏感性在T _c处变得发散。与其他非聚类方法相比，该方法得到的 Ising 模型的临界温度相当好。将此方法扩展到更复杂的自旋模型很简单，例如具有连续对称性。