On the Riemann-Hilbert approach to the asymptotic analysis of the   correlation functions of the Quantum Nonlinear Schrodinger equation. Non-free   fermionic case
  We consider the local field dynamical temperature correlation function of the Quantum Nonlinear Schrodinger equation with the finite coupling constant. This correlation function admits a Fredholm determinant representation. The related operator-valued Riemann--Hilbert problem is used for analysing the leading term of the large time and long distance asymptotics of the correlation function. 
A. R. Its (Department of Mathematical Sciences IUPUI, Indianapolis,   USA) and N. A. Slavnov (Steklov Mathematical Institute...