A note on the Chevalley-Eilenberg Cohomology for the Galilei and   Poincare Algebras
  We construct in a systematic way the complete Chevalley-Eilenberg cohomology at form degree two, three and four for the Galilei and Poincare groups. The corresponding non-trivial forms belong to certain representations of the spatial rotation (Lorentz) group. In the case of two forms they give all possible central and non-central extensions of the Galilei group (and all non-central extensions of the Poincare group). The procedure developed in this paper can be applied to any space-time symmetry group. 
Sotirios Bonanos and Joaquim Gomis