  In the framework of the quantum inverse scattering method, we consider a
problem of constructing local operators for two-dimensional quantum integrable
models, especially for the lattice versions of the nonlinear Schrodinger and
sine-Gordon models. We show that a certain class of local operators can be
constructed from the matrix elements of the monodromy matrix in a simple way.
They are closely related to the quantum projectors and have nice commutation
relations with the half of the matrix elements of the elementary monodromy
matrix. The form factors of these operators can be calculated by using the
standard algebraic Bethe ansatz techniques.

High Energy Physics - Theory