On form factors of boundary changing operators

TL;DR

This paper develops a bootstrap approach to compute form factors of boundary condition changing operators, interpreting boundary changes as local quenches and providing a method to analyze state overlaps in integrable models.

Contribution

It introduces axioms for boundary changing operator form factors and solves them explicitly in free boson and Lee-Yang models.

Findings

Form factors determined for free boson and Lee-Yang models.

Boundary condition changes interpreted as local quenches.

Provides a framework for overlap calculations in boundary integrable systems.

Abstract

We develop a form factor bootstrap program to determine the matrix elements of local, boundary condition changing operators. We propose axioms for these form factors and determine their solutions in the free boson and Lee-Yang models. The sudden change in the boundary condition, caused by an operator insertion, can be interpreted as a local quench and the form factors provide the overlap of any state before the quench with any outgoing state after the quench.