Factorized Scattering in the Presence of Reflecting Boundaries
A. Fring, R. Köberle
TL;DR
This work develops an exact framework for factorized scattering in integrable 2D quantum field theories with reflecting boundaries by extending the Zamolodchikov algebra to include a wall operator $W$. The authors derive the factorization and inhomogeneous bootstrap equations that constrain $W$ in terms of bulk $S$-matrices, and they show that $W$ factorizes into blocks in one-to-one correspondence with the $S$-matrix blocks. For concrete affine Toda theories (Bullough-Dodd, $A_2^{(1)}$, and $A_4^{(2)}$), explicit constructions of the $W$-matrix are provided, including Gamma-product representations for the constituent blocks, with all examples lacking poles or zeros in the physical sheet, implying elastic boundary scattering. The results demonstrate a parallel structure between bulk and boundary scattering and provide exact tools for analyzing finite-volume integrable models with reflecting boundaries, including connections to minimal two-particle form factors.
Abstract
We formulate a general set of consistency requirements, which are expected to be satisfied by the scattering matrices in the presence of reflecting boundaries. In particular we derive an equivalent to the boostrap equation involving the W-matrix, which encodes the reflection of a particle off a wall. This set of equations is sufficient to derive explicit formulas for $W$, which we illustrate in the case of some particular affine Toda field theories.
