Creation of Elko particles in asymptotically expanding universe

TL;DR

This paper investigates the creation of Elko spinor particles due to universe expansion, deriving analytic solutions for their production spectrum and comparing it to scalar and Dirac particles, with implications for dark matter.

Contribution

It provides the first analytic approximation for Elko particle creation in an expanding universe and compares their production to scalar and Dirac particles.

Findings

Lighter Elko particles are produced in larger quantities than Dirac fermions.

The particle spectrum generalizes the scalar field case, reducing to it under certain conditions.

More light Elko particles are created gravitationally, supporting their role as dark matter candidates.

Abstract

In the present article we study the process of particle creation for Elko spinor fields as a consequence of expansion of the universe. We study the effect driven by a expanding background that is asymptotically minkowskian in the past and future. The differential equation that governs the time mode function is obtained for the conformal coupling case and, although its solution is non-analytic, within an approximation that preserves the characteristics of the terms that break the analyticity, analytic solutions are obtained. Thus, by means of the Bogolyubov transformations technique, the number density of particles created is obtained, which can be compared to exact solutions already present in literature for scalar and Dirac particles. The spectrum of created particles is obtained and it was found that it is a generalization of the scalar field case, which converges to the scalar field one when the specific terms concerning the Elko field are dropped out. We also found that lighter Elko particles are created in larger quantities than Dirac fermionic particles. By considering the Elko particles as candidate to dark matter in the universe, such result shows that there are more light dark matter (Elko) particles created by gravitational effects in the universe than baryonic (fermionic) matter, in agreement to standard model.