Cosmic rays from annihilation of heavy dark matter particles

TL;DR

This paper proposes a novel dark matter annihilation mechanism involving heavy fermions created by scalaron decay in modified gravity, potentially explaining ultra-high-energy cosmic rays beyond astrophysical sources.

Contribution

It introduces a new scenario where dark matter particles slightly below half the scalaron mass produce cosmic rays via annihilation, linking modified gravity to cosmic ray origins.

Findings

The scenario can account for observed ultra-high-energy cosmic rays.

Resonance annihilation into energetic light particles is feasible.

Dark matter density regions influence annihilation rates.

Abstract

The origin of the ultra high energy cosmic rays via annihilation of heavy stable, fermions "f", of the cosmological dark matter (DM) is studied. The particles in question are supposed to be created by the scalaron decays in $R^2$ modified gravity. Novel part of our approach is the assumption that the mass of these carriers of DM is slightly below than a half of the scalaron mass. In such a case the phase space volume becomes tiny. It leads to sufficiently low probability of "f" production, so their average cosmological energy density could be equal to the observed energy density of dark matter. Several regions of the universe, where the annihilation could take place, are studied. They include the whole universe under assumption of homogeneous energy density, the high density DM clump in the galactic centre, the cloud of DM in the Galaxy with realistic density distribution, and high density clusters of DM in the Galaxy. Possible resonance annihilation of $f \bar f$ into energetic light particle is considered. We have shown that the proposed scenario can successfully explain the origin of the ultrahigh energy flux of cosmic rays where the canonical astrophysical mechanisms are not operative.