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arXiv 1706.00799cond-mat.stat-mech
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正方形格上生成树与伊辛模型的对应

Correspondence between spanning trees and the Ising model on a square lattice

G. M. Viswanathan

备注：
Subm. to Phys. Rev. E
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摘要：

在统计物理学中的一个重要问题涉及到平衡统计力学中研究的格点模型的配分函数与图论计数问题之间的迷人联系。本文研究了正方格上伊辛模型的生成树个数与配分函数之间的关系。生成树生成函数$T(z)$在$z=1$处求值时给出生成树常数，而在微分时给出格点格林函数。已知对于无限正方形晶格，在临界温度$K=K_c$下计算的伊辛模型的配分函数$Z(K)$与$T(1)$有关。在这里，我们表明，这一想法实际上推广到所有的实际温度。我们证明了$ ( Z(K) {\rm sech~} 2K ~\!)^2 = k \exp\big[ T(k) \big] $，其中$k= 2 \tanh(2K) {\rm sech}(2K)$ .相同的马勒测度连接了两个看似不同的量$T(z)$和$Z(K)$。反过来，马勒测度由随机游走结构函数确定。最后，我们证明了上述对应关系并不以简单的方式推广到非平面格。

英文摘要：

An important problem in statistical physics concerns the fascinating connections between partition functions of lattice models studied in equilibrium statistical mechanics on the one hand and graph theoretical enumeration problems on the other hand. We investigate the nature of the relationship between the number of spanning trees and the partition function of the Ising model on the square lattice. The spanning tree generating function $T(z)$ gives the spanning tree constant when evaluated at $z=1$, while giving he lattice green function when differentiated. It is known that for the infinite square lattice the partition function $Z(K)$ of the Ising model evaluated at the critical temperature $K=K_c$ is related to $T(1)$. Here we show that this idea in fact generalizes to all real temperatures. We prove that $ ( Z(K) {\rm sech~} 2K ~\!)^2 = k \exp\big[ T(k) \big] $, where $k= 2 \tanh(2K) {\rm sech}(2K)$. The identical Mahler measure connects the two seemingly disparate quantities $T(z)$ and $Z(K)$. In turn, the Mahler measure is determined by the random walk structure function. Finally, we show that the the above correspondence does not generalize in a straightforward manner to non-planar lattices.

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