Fermion production in a magnetic field in a de Sitter Universe

TL;DR

This paper investigates fermion production in a magnetic field within a de Sitter universe, revealing that production is significant during early universe expansion and depends on the magnetic field orientation and expansion rate.

Contribution

It provides an exact solution-based analysis of fermion production in a magnetic field in de Sitter space, highlighting the conditions and probabilities of such processes.

Findings

Fermion production is most probable perpendicular to the magnetic field.

Production probability increases with the universe's expansion rate.

In the Minkowski limit, fermion production is forbidden.

Abstract

The process of fermion production in the field of a magnetic dipole on a de Sitter expanding universe is analyzed. The amplitude and probability for production of massive fermions are obtained using the exact solution of the Dirac equation written in the momentum-helicity basis. We found that the most probable transitions are those that generate the fermion pair perpendicular to the direction of the magnetic field. The behavior of the probability is graphically studied for large/small values of the expansion factor, and a detailed analysis of the probability in terms of the angle between the momenta vectors of the particle and antiparticle is performed. The phenomenon of fermion production is significant only at large expansion which corresponds to the conditions from the early Universe. When the expansion factor vanishes we recover the Minkowski limit where this process is forbidden by the simultaneous energy-momentum conservation.