Chiral fermions and torsion in the early Universe

Abstract arising from fermionic matter in the Einstein-Cartan formulation of general relativity is considered in the context of Robertson-Walker geometries and the early Universe. An ambiguity in the way torsion arising from hot fermionic matter in chiral models should be implemented is highlighted and discussed. In one interpretation, the non-zero torsion present in chiral models gives a negative contribution to the energy density which ameliorates the Big Bang singularity or even, in extreme cases, eliminates it completely giving bounce solutions for early Universe cosmology. It is often the case that quantum matter acts as a source for a classical field in situations where quantum aspects of the field itself can be ignored. This approximation has proven extremely useful for Einstein's equations where