Excited states by analytic continuation of TBA equations

TL;DR

This paper introduces a novel method using analytic continuation of TBA equations to compute excited states in integrable models, validated by numerical results and asymptotic analysis.

Contribution

It presents a new approach to derive integral equations for excited states from ground state TBA equations via analytic continuation.

Findings

Derived equations for excited states in the scaling Lee-Yang model.

Numerical results agree well with truncated conformal space approach.

Provided analytical insights into ultraviolet and infrared asymptotics.

Abstract

We suggest an approach to the problem of finding integral equations for the excited states of an integrable model, starting from the Thermodynamic Bethe Ansatz equations for its ground state. The idea relies on analytic continuation through complex values of the coupling constant, and an analysis of the monodromies that the equations and their solutions undergo. For the scaling Lee-Yang model, we find equations in this way for the one- and two- particle states in the spin-zero sector, and suggest various generalisations. Numerical results show excellent agreement with the truncated conformal space approach, and we also treat some of the ultraviolet and infrared asymptotics analytically.