ELKO fermions as dark matter candidates

TL;DR

This paper investigates ELKO fermions as potential cold dark matter candidates, analyzing their interactions, experimental constraints, and astrophysical implications, ultimately finding limited viability for their role in dark matter.

Contribution

It provides the first comprehensive analysis of ELKO fermions as dark matter, including coupling limits and astrophysical constraints, highlighting their limited contribution.

Findings

Astrophysical and cosmological constraints largely exclude ELKO as significant dark matter.

ELKO can only contribute if it was never in thermal equilibrium with the cosmic plasma.

A relationship between ELKO self-coupling and mass is established based on galactic core observations.

Abstract

We study the implications of the ELKO fermions as a cold dark matter candidate. Such fermions arise in theories that are not symmetric under the full Lorentz group. Although they do not carry electric charge, ELKOs can still couple to photons through a nonstandard interaction. They also couple to the Higgs but do not couple to other standard model particles. We impose limits on their coupling strength and the ELKO mass assuming that these particles give dominant contribution to the cosmological cold dark matter. We also determine limits imposed by the direct dark matter search experiments on the ELKO-photon and the ELKO-Higgs coupling. Furthermore we determine the limit imposed by the gamma ray bursts time delay observations on the ELKO-Higgs coupling. We find that astrophysical and cosmological considerations rule out the possibility that ELKO may contribute significantly as a cold dark matter candidate. The only allowed scenario in which it can contribute significantly as a dark matter candidate is that it was never in equilibrium with the cosmic plasma. We also obtain a relationship between the ELKO self-coupling and its mass by demanding it to be consistent with observations of dense cores in the galactic centers.