Energy Momentum Tensor and Operator Product Expansion in Local Causal   Perturbation Theory
  We derive new examples for algebraic relations of interacting fields in local perturbative quantum field theory. The fundamental building blocks in this approach are time ordered products of free (composed) fields. We give explicit formulas for the construction of Poincare covariant ones, which were already known to exist through cohomological arguments.   For a large class of theories the canonical energy momentum tensor is shown to be conserved. Classical theories without dimensionful couplings admit an improved tensor that is additionally traceless. On the example of phi^4-theory we discuss the improved tensor in the quantum theory. Its trace receives an anomalous contribution due to its conservation.   Moreover we define an interacting bilocal normal product for scalar theories. This leads to an operator product expansion of two time ordered fields. 
Dirk Prange