Galactic 511 keV line from MeV millicharged dark matter

TL;DR

This paper proposes that a light, millicharged fermion could explain the 511 keV gamma-ray anomaly observed in the galactic bulge, fitting within existing relic density and collider constraints.

Contribution

It introduces a novel millicharged fermion model to account for the 511 keV gamma-ray line, connecting astrophysical observations with particle physics constraints.

Findings

Millicharged fermion can produce positrons explaining the 511 keV line.

Parameter space exists where relic density and collider constraints are satisfied.

The model provides a viable dark matter candidate linked to gamma-ray observations.

Abstract

We present a possible explanation of the recently observed 511 keV $\gamma$-ray anomaly with a new ``millicharged'' fermion. The new fermion is light (${\cal O}({\rm MeV})$) but has never been observed by any collider experiments mainly because of its tiny electromagnetic charge $\epsilon e$. We show that constraints from its relic density in the Universe and collider experiments allow a parameter range such that the 511 keV cosmic $\gamma$-ray emission from the galactic bulge may be due to positron production from this millicharged fermion.