On a generalised Lambert $W$ branch transition function arising from $p,q$-binomial coefficients

Abstract

With only a complete solution in dimension one and partially solved in dimension two, the Lenz-Ising model of magnetism is one of the most studied models in theoretical physics. An approach to solving this model in the high-dimensional case ($d>4$) is by modelling the magnetisation distribution with $p,q$-binomial coefficients. The connection between the parameters $p,q$ and the distribution peaks is obtained with a transition function $\omega$ which generalises the mapping of Lambert $W$ function branches $W_0$ and $W_{-1}$ to each other. We give explicit formulas for the branches for special cases. Furthermore, we find derivatives, integrals, parametrizations, series expansions, and asymptotic behaviors.