On the diagonal susceptibility of the two-dimensional Ising model

Articles you may be interested in Social applications of two-dimensional Ising models Am. The critical temperature of two-dimensional and three-dimensional Ising models Am. The critical renormalized coupling constants in the symmetric phase of the three dimensional Ising model AIP Conf. We consider the diagonal susceptibility of the isotropic 2D Ising model for temperatures below the critical temperature. For a parameter k related to temperature and the interaction constant, we extend the diagonal susceptibility to complex k inside the unit disc, and prove the conjecture that the unit circle is a natural boundary.