Sub-MeV Bosonic Dark Matter, Misalignment Mechanism and Galactic Dark Matter Halo Luminosities

TL;DR

This paper investigates sub-MeV bosonic dark matter particles created by the misalignment mechanism, analyzing their decay signatures and potential detectability through photon spectra in galaxy halos.

Contribution

It introduces the decay signatures of axion-like particles and dark photons as dark matter candidates, highlighting their detectability via photon emissions.

Findings

Decaying photon signals are potentially observable with current technology.

Photon spectra from decays are monochromatic or heavily peaked, aiding detection.

Decay processes are analogous to orthopositronium decay physics.

Abstract

We explore a scenario that the dark matter is a boson condensate created by the misalignment mechanism, in which a spin 0 boson (an axion-like particle) and a spin 1 boson (the dark photon) are considered, respectively. We find that although the sub-MeV dark matter boson is extremely stable, the huge number of dark matter particles in a galaxy halo makes the decaying signal detectable. A galaxy halo is a large structure bounded by gravity with a typical $\sim10^{12}$ solar mass, and the majority of its components are made of dark matter. For the axion-like particle case, it decays via $\phi\to \gamma\gamma$, therefore the photon spectrum is monochromatic. For the dark photon case, it is a three body decay $A'\to\gamma\gamma\gamma$. However, we find that the photon spectrum is heavily peaked at $M/2$ and thus can facilitate observation. We also suggest a physical explanation for the three body decay spectrum by comparing the physics in the decay of orthopositronium. In addition, for both cases, the decaying photon flux can be measured for some regions of parameter space using current technologies.