Cosmological Bounces Induced by a Fermion Condensate

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 $⟨\bar{\Psi }\Psi ⟩$ -- 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.

arXiv comment5 pages, 4 figures; to appear in PRL

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• Probability of the Initial Conditions for Inflation and Slow Contraction
• Covariant single-field formulation of effective cosmological bounces
• Fermionic quantum cosmology as a framework for resolving type IV singularities