The Form Factor Program: a Review and New Results – the Nested $\mathrm{SU}(N)$ Off-Shell Bethe Ansatz

The purpose of the “bootstrap program” for integrable quantum field theories in $1+1$ dimensions is to construct explicitly a model in terms of its Wightman functions. In this article, this program is mainly illustrated in terms of the sinh-Gordon model and the $SU(N)$ Gross–Neveu model. The nested off-shell Bethe ansatz for an $SU( N)$ factorizing S-matrix is constructed. We review some previous results on sinh-Gordon form factors and the quantum operator field equation. The problem of how to sum over intermediate states is considered in the short distance limit of the two point Wightman function for the sinh-Gordon model.