Haag’s theorem in noncommutative quantum field theory

Haag’s theorem was extended to the general case of noncommutative quantum field theory 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 the other theory is equal to unity as well. In fact, this result is valid in any SO (1, 1)-invariant quantum field theory, an important example of which is noncommutative quantum field theory.