Quantum field theory arises from the requirement that the S-matrix is lorentz scalar and obeys the cluster decomposition principle.
I want to know if there are other ways to build invariant S-Matrices that obey the cluster decomposition principle without using quantum field theory. QFT is the most natural way to do it but I'm interested in other possible approaches.
This post imported from StackExchange Physics at 2014-08-11 14:52 (UCT), posted by SE-user nabil