The angular momentum of the gravitational field and the Poincare group
  We redefine the gravitational angular momentum in the framework of the teleparallel equivalent of general relativity. In similarity to the gravitational energy-momentum, the new definition for the gravitational angular momentum is coordinate independent. By considering the Poisson brackets in the phase space of the theory, we find that the gravitational energy-momentum and angular momentum correspond to a representation of the Poincar\'e group. This result allows us to define Casimir type invariants for the gravitational field. 
J. W. Maluf, S. C. Ulhoa, F. F. Faria and J. F. da Rocha-Neto