Confronting the Galactic 511 keV emission with $B-L$ gauge boson dark matter

TL;DR

This paper proposes a $B-L$ gauge boson as a small component of dark matter that can explain the Galactic 511 keV emission through decay, linking particle physics with astrophysical observations and GUT-scale physics.

Contribution

It introduces a $B-L$ gauge boson dark matter model that explains the Galactic positron line and constrains its parameters within a GUT-scale symmetry breaking framework.

Findings

Bounds on gauge boson mass and positron injection energy consistent with observations.

Predicted $B-L$ breaking scale around $10^{15}$--$10^{16}$ GeV.

Model aligns with seesaw mechanism and leptogenesis theories.

Abstract

The $B-L$ gauge symmetry motivated from the successful generation of the seesaw mechanism and leptogenesis. We show that if the $B-L$ gauge boson constitutes a small fraction of the dark matter (DM) it can explain the Galactic $511$ keV emission via the decay into an electron-positron pair. We find the model parameter space that is consistent with the seesaw mechanism, cosmologically viable, and accounting for the amplitude of the Galactic positron line. From this parameter space we derive an upper bound of the gauge boson mass and then an bound of the positron injection energy $\lesssim3$ MeV. This derived energy bound is consistent with the observational upper limit of the injection energy. The resultant model predicts the $B-L$ breaking scale to be in a relatively narrow range, i.e., $V_{B\textrm{--}L}\sim10^{15} \textrm{--} 10^{16} $GeV, which is consistent with a Grand Unification (GUT) scale seesaw mechanism. The model is consistent in several phenomenologies, suggesting their common origin from the B-L symmetry breaking.