Friedmann-like universes with torsion

We consider spatially homogeneous and isotropic cosmologies with non-zero torsion. Given the high symmetry of these universes, we adopt a specific form for the torsion tensor that preserves the homogeneity and isotropy of the spatial hypersurfaces. Employing both covariant and metric-based techniques, we derive the torsional analogs of the continuity, Friedmann and, Raychaudhuri equations. These formulae demonstrate how, by playing the role of the spatial curvature, or that of the cosmological constant, torsion can drastically change the standard evolution of Friedmann-like cosmologies. For instance, torsion alone can lead to exponential inflationary expansion. Also, in the presence of torsion, the Milne universe evolves very much like the de Sitter model. Turning our attention to static spacetimes, we find that there exist torsional analogs of the classic Einstein static universe, with all three types of spatial curvature. Finally, we use perturbative methods to test the stability of the static solution in the presence of torsion. Our results show that stability is possible, provided the torsion field and the universe's spatial curvature have the appropriate profiles.