Modular covariant torus partition functions of dense $A_1^{(1)}$ and dilute $A_2^{(2)}$ loop models

TL;DR

This paper derives and compares the modular covariant torus partition functions of dense and dilute loop models, revealing their equivalence and universality class, with implications for related integrable models.

Contribution

It conjectures the scaling limits of transfer matrix traces and expresses the partition functions in terms of known functions, establishing their equivalence for dense and dilute models.

Findings

Partition functions are identical for dense and dilute models.

Partition functions are expressed as sesquilinear forms in Verma characters.

Partition functions match for related 6-vertex and 19-vertex models.

Abstract

Yang-Baxter integrable dense $A_1^{(1)}$ and dilute $A_2^{(2)}$ loop models are considered on the torus in their simplest physical regimes. A combination of boundary conditions $(h,v)$ is applied in the horizontal and vertical directions with $h,v=0$ and $1$ for periodic and antiperiodic boundary conditions respectively. The fugacities of non-contractible and contractible loops are denoted by $\alpha$ and $\beta$ respectively where $\beta$ is simply related to the crossing parameter $\lambda$. At roots of unity, when $\lambda/\pi\in\mathbb Q$, these models are the dense ${\cal LM}(p,p')$ and dilute ${\cal DLM}(p,p')$ logarithmic minimal models with $p,p'$ coprime integers. We conjecture the scaling limits of the transfer matrix traces in the standard modules with $d$ defects and deduce the conformal partition functions ${\cal Z}_{\textrm{dense}}^{(h,v)}(\alpha)$ and ${\cal Z}_{\textrm{dilute}}^{(h,v)}(\alpha)$ using Markov traces. These are expressed in terms of functions ${\cal Z}_{m,m'}(g)$ known from the Coulomb gas arguments of Di Francesco, Saleur and Zuber and subsequently as sesquilinear forms in Verma characters. Crucially, we find that the partition functions are identical for the dense and dilute models. The coincidence of these conformal partition functions provides compelling evidence that, for given $(p,p')$, these dense and dilute theories lie in the same universality class. In root of unity cases with $\alpha=2$, the $(h,v)$ modular covariant partition functions are also expressed as sesquilinear forms in affine $u(1)$ characters involving generalized Bezout conjugates. These also give the modular covariant partition functions for the 6-vertex and Izergin-Korepin 19-vertex models in the corresponding regimes.