Form factors in the finite volume

We study exactly solvable models of quantum statistical mechanics. Our main example is the Quantum nonlinear Schrodinger equation. This model can be solved by algebraic Bethe Ansatz. We are interested in the expression for a form factor of the local field in the finite volume F_N = 〈0| Π_j=1^N C(μ_j)ψ(0, 0) Π _j=1^N+1 B(λ_j)|0〉. We found a determinant representation for this form factor. We think that this is the universal feature: finite volume form factor of any exactly solvable model can be represented a determinant.