Haag's Theorem in Noncommutative Quantum Field Theory
  Haag's theorem was extended to noncommutative quantum field theory in a general case when time does not commute with spatial variables. It was proven that if S-matrix is equal to unity in one of two theories related by unitary transformation, then the corresponding one in another theory is equal to unity as well. In fact this result is valid in any SO(1,1) invariant quantum field theory, of which an important example is noncommutative quantum field theory. 
K. V. Antipin, M. N. Mnatsakanova, Yu. S. Vernov
math-ph hep-th math.MP