On nonequilibrium states in QFT model with boundary interaction
  We prove that certain nonequilibrium expectation values in the boundary sine-Gordon model coincide with associated equilibrium-state expectation values in the systems which differ from the boundary sine-Gordon in that certain extra boundary degrees of freedom (q-oscillators) are added. Applications of this result to actual calculation of nonequilibrium characteristics of the boundary sine-Gordon model are also discussed. 
V. Bazhanov, S. Lukyanov, A. Zamolodchikov