Comment on "Fermion production in a magnetic field in a de Sitter universe"

TL;DR

This paper critiques a recent calculation of fermion pair creation in de Sitter space, highlighting gauge dependence issues in the transition probabilities used in the perturbative approach.

Contribution

It identifies gauge dependence in the transition probabilities and analyzes the source of this problem in the nonoscillatory fermion current behavior at infinite times.

Findings

Transition probabilities are gauge dependent.

Gauge variations are linked to nonoscillatory fermion currents.

The problem arises from assumptions about decoupling at infinite times.

Abstract

We point out that the transition probabilities used in a recent perturbative calculation of pair creation in an external magnetic field in the expanding de Sitter space with the $in$ and $out$ fermion states defined by the Bunch-Davies modes [C. Crucean et al., Phys. Rev. D 73 044019 (20016)] are gauge dependent quantities. We examine the gauge variations of these amplitudes assuming a decoupling of the interaction at infinite times, which allows to conclude that the source of the problem lies in the nonoscillatory behavior of the fermion current in the infinite future.