  Anomalous contributions to the energy-momentum commutators are calculated for
even dimensions, by using a non-perturbative approach that combines operator
product expansion and Bjorken-Johnson-Low limit techniques. We first study the
two dimensional case and give the covariant expression for the commutators. The
expression in terms of light-cone coordinates is then calculated and found to
be in perfect agreement with the results in the literature. The particular
scenario of the light-cone frame is revisited using a reformulation of the BJL
limit in such a frame. The arguments used for $n=2$ are then generalized to the
case of any even dimensional Minkowskian spacetime and it is shown that there
are no anomalous contributions to the commutators for $n\not=2$. These results
are found to be valid for both fermionic and bosonic free fields. A
generalization of the BJL-limit is later used to obtain double commutators of
energy-momentum tensors and to study the Jacobi identity. The two dimensional
case is studied and we find no existance of 3-cocycles in both the Abelian and
non-Abelian case.
