On Cosmological Spacetime Structure and Symmetry: Manifold as a Lie   Group, Spinor Structure and Symmetry Group, Minkowski Metric, and   Unnecessariness of Double-Valued Representations
  It is shown that cosmological spacetime manifold has the structure of a Lie group and a spinor space. This leads naturally to the Minkowski metric on tangent spaces and the Lorentzian metric on the manifold and makes it possible to dispense with double-valued representations. 
Vladimir S. Mashkevich (CUNY)