F\'eeton ($B-L$ Gauge Boson) Dark Matter for the 511-keV Gamma-Ray Excess and the Prediction of Low-energy Neutrino Flux

TL;DR

This paper proposes that a very light gauge boson called féeton, associated with the $U(1)_{B-L}$ symmetry, can explain the 511-keV gamma-ray excess through its decay into electron-positron pairs and predicts detectable low-energy neutrino flux.

Contribution

It introduces the féeton as a dark matter candidate with a specific decay mechanism explaining gamma-ray excess and predicts associated neutrino signals for future detection.

Findings

Féeton decay explains the Galactic 511-keV gamma-ray excess.

Predicted neutrino flux could be detected with future low-energy experiments.

Féeton lifetime is consistent with cosmological constraints.

Abstract

The f\'eeton is the gauge boson of the $U(1)_{B-L}$ gauge theory. If the gauge coupling constant is extremely small, it becomes a candidate for dark matter. We show that its decay to a pair of electron and positron explains the observed Galactic 511-keV gamma-ray excess in a consistent manner. This f\'eeton dark matter decays mainly into pairs of neutrino and anti-neutrino. Future low-energy experiments with improved directional capability make it possible to capture those neutrino signals. The seesaw-motivated parameter space predicts a relatively short f\'eeton lifetime comparable to the current cosmological constraint.