Cosmological Bounces Induced by a Fermion Condensate

TL;DR

This paper demonstrates that fermion condensation can induce a smooth, non-singular cosmological bounce, connecting contraction and expansion phases without requiring high fermion densities, thus avoiding anisotropy issues.

Contribution

It introduces a novel mechanism where fermion condensates trigger a cosmological bounce, avoiding anisotropy problems associated with high-density fermion states.

Findings

Fermion condensation can produce a non-singular bounce.

A chiral condensate forms spontaneously after slow contraction.

The mechanism avoids large anisotropy and chaotic behavior.

Abstract

We show that it is possible for fermion condensation of the Nambu-Jona-Lasinio type to induce a non-singular bounce that smoothly connects a phase of slow contraction to a phase of expansion. A chiral condensate -- a non-zero vacuum expectation value of the spinor bilinear $\langle \bar{\Psi}\Psi \rangle$ -- can form spontaneously after a slow contraction phase smooths and flattens the universe and the Ricci-curvature exceeds a critical value. In this approach, a high density of spin-aligned free fermions is not required, which avoids the problem of generating a large anisotropy and initiating chaotic mixmaster behavior during the bounce phase.