Gravitational fermion creation during an anisotropic phase of cosmological expansion

TL;DR

This paper demonstrates that anisotropic early universe conditions can lead to fermionic particle creation, including massless particles, with significant implications for cosmology and dark matter.

Contribution

It provides the first analysis of fermion creation in an anisotropic universe, highlighting the possibility of massless fermion production unlike in isotropic models.

Findings

Massless fermion production occurs in anisotropic spacetime.

Created particles can significantly influence early universe dynamics.

Potential implications for dark matter and primordial magnetic fields.

Abstract

The free Dirac equation is solved in a Bianchi Type I space-time, which represents a homogeneous but anisotropic universe, to show the creation of fermionic particles. It is found that unlike in the isotropic case, massless fermion production is possible. An estimate of the energy density of massless particles created during an early anisotropic phase of cosmological expansion is shown to cause substantial back-reaction on the gravitational field. The potential relevance to dark matter particle production, primordial magnetogenesis, and early universe cosmology is discussed briefly.