Excited-state thermodynamics

TL;DR

This paper introduces a method to compute excited-state energies in 1+1-dimensional integrable models by modifying boundary conditions and calculating thermodynamic expectation values, demonstrated across various models.

Contribution

It presents a novel approach to determine excited states in integrable models through boundary condition modifications and symmetry operator expectations.

Findings

Method successfully applied to multiple models

Enables calculation of excited-state energies

Provides insights into boundary condition effects

Abstract

In the last several years, the Casimir energy for a variety of 1+1-dimensional integrable models has been determined from the exact S-matrix. It is shown here how to modify the boundary conditions to project out the lowest-energy state, which enables one to find excited-state energies. This is done by calculating thermodynamic expectation values of operators which generate discrete symmetries. This is demonstrated with a number of perturbed conformal field theories, including the Ising model, the three-state Potts model, ${\bf Z}_n$ parafermions, Toda minimal S-matrices, and massless Goldstinos.