Description
We discuss the role of the Cartan torsion tensor in Riemann metric geometry in view of the Sciama-Kibble completion of Einstein gravity, in the case in which Dirac fields are considered; we review various models in which the spin may be as important as the energy for the dynamics of matter fields: we present some of the effects of this enlarged dynamics in concomitance to the avoidance of singularity formation and a simple solution to the cosmological constant problem.