Gravitational Energy-Momentum in the Tetrad and Quadratic Spinor   Representations of General Relativity
  In the Tetrad Representation of General Relativity, the energy-momentum expression, found by Moller in 1961, is a tensor wrt coordinate transformations but is not a tensor wrt local Lorentz frame rotations. This local Lorentz freedom is shown to be the same as the six parameter normalized spinor degrees of freedom in the Quadratic Spinor Representation of General Relativity. From the viewpoint of a gravitational field theory in flat space-time, these extra spinor degrees of freedom allow us to obtain a local energy-momentum density which is a true tensor over both coordinate and local Lorentz frame rotations. 
Roh S. Tung (CIPA and Univ of Chicago), James M. Nester (National   Central Univ, Taiwan)