Integrable Structure of Conformal Field Theory II. Q-operator and DDV equation

TL;DR

This paper constructs Q-operators in conformal field theory that satisfy Baxter's T-Q relation, derives DDV equations for their eigenvalues, and explores their asymptotics and applications to quantum Hall transport.

Contribution

It introduces explicit construction of Q-operators in CFT, establishes their relation to DDV equations, and connects these to quantum Hall transport phenomena.

Findings

Q-operators commute and satisfy Baxter's T-Q relation.

DDV equations derived for Q-operator eigenvalues.

Asymptotic expansions include dual nonlocal integrals of motion.

Abstract

This paper is a direct continuation of\ \BLZ\ where we begun the study of the integrable structures in Conformal Field Theory. We show here how to construct the operators ${\bf Q}_{\pm}(\lambda)$ which act in highest weight Virasoro module and commute for different values of the parameter $\lambda$. These operators appear to be the CFT analogs of the $Q$ - matrix of Baxter\ \Baxn, in particular they satisfy famous Baxter's ${\bf T}-{\bf Q}$ equation. We also show that under natural assumptions about analytic properties of the operators ${\bf Q}(\lambda)$ as the functions of $\lambda$ the Baxter's relation allows one to derive the nonlinear integral equations of Destri-de Vega (DDV)\ \dVega\ for the eigenvalues of the ${\bf Q}$-operators. We then use the DDV equation to obtain the asymptotic expansions of the ${\bf Q}$ - operators at large $\lambda$; it is remarkable that unlike the expansions of the ${\bf T}$ operators of \ \BLZ, the asymptotic series for ${\bf Q}(\lambda)$ contains the ``dual'' nonlocal Integrals of Motion along with the local ones. We also discuss an intriguing relation between the vacuum eigenvalues of the ${\bf Q}$ - operators and the stationary transport properties in boundary sine-Gordon model. On this basis we propose a number of new exact results about finite voltage charge transport through the point contact in quantum Hall system.