On form factors of boundary changing operators

Understand

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.