Nonsingular, big-bounce cosmology from spinor-torsion coupling

TL;DR

This paper demonstrates that incorporating spinor-torsion coupling in Einstein-Cartan theory replaces the big bang singularity with a big bounce, providing a nonsingular cosmological model consistent with observed large-scale flatness and isotropy.

Contribution

It introduces a cosmological model where spinor-torsion interactions prevent singularities, offering a new approach to early universe dynamics beyond standard general relativity.

Findings

Replaces big bang singularity with a finite bounce

Explains large-scale flatness and isotropy of the universe

Highlights significance of spin-torsion coupling at high densities

Abstract

The Einstein-Cartan-Sciama-Kibble theory of gravity removes the constraint of general relativity that the affine connection be symmetric by regarding its antisymmetric part, the torsion tensor, as a dynamical variable. The minimal coupling between the torsion tensor and Dirac spinors generates a spin-spin interaction which is significant in fermionic matter at extremely high densities. We show that such an interaction averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting. This scenario also explains why the present Universe at largest scales appears spatially flat, homogeneous and isotropic.