A nonlinear identity for the scattering phase of integrable models

The scattering phase of quantum integrable models is found from linear integral equations of a special type. Solutions of these equations satisfy some nonlinear identities, which, in particular, relate the values of the scattering phase at the boundaries of the Fermi sphere. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 116, No. 3, pp. 362–366, September, 1998.