Associative-algebraic approach to logarithmic conformal field theories

TL;DR

This paper develops an algebraic framework to analyze logarithmic conformal field theories derived from lattice models, specifically spin chains with supersymmetry, revealing their boundary CFT structures and fusion rules.

Contribution

It introduces an associative-algebraic approach to study boundary CFTs from lattice models, providing detailed examples and deriving fusion rules for indecomposable Virasoro modules.

Findings

Boundary CFTs with c=-2 and c=0 identified as limits of specific spin chains.

Fusion rules for boundary fields derived from lattice models.

Submodule structures of Virasoro representations explicitly characterized.

Abstract

We set up a strategy for studying large families of logarithmic conformal field theories by using the enlarged symmetries and non--semi-simple associative algebras appearing in their lattice regularizations (as discussed in a companion paper). Here we work out in detail two examples of theories derived as the continuum limit of XXZ spin-1/2 chains, which are related to spin chains with supersymmetry algebras gl($n|n$) and gl($n+1|n$), respectively, with open (or free) boundary conditions in all cases. These theories can also be viewed as vertex models, or as loop models. Their continuum limits are boundary conformal field theories (CFTs) with central charge $c=-2$ and $c=0$ respectively, and in the loop interpretation they describe dense polymers and the boundaries of critical percolation clusters, respectively. We also discuss the case of dilute (critical) polymers as another boundary CFT with $c=0$. Within the supersymmetric formulations, these boundary CFTs describe the fixed points of certain nonlinear sigma models that have a supercoset space as the target manifold, and of Landau-Ginzburg field theories. The submodule structures of indecomposable representations of the Virasoro algebra appearing in the boundary CFT, representing local fields, are derived from the lattice. A central result is the derivation of the fusion rules for these fields.