Enhanced Rare Pion Decays from a Model of MeV Dark Matter

TL;DR

This paper proposes a MeV-scale dark matter model involving a light vector boson that explains galactic gamma-ray signals and predicts enhanced rare pion decay rates, aligning with recent experimental anomalies.

Contribution

It introduces a novel dark matter model with a light vector boson that links galactic gamma-ray observations to rare pion decay enhancements, consistent with experimental data.

Findings

The model explains the 511 keV gamma-ray line from the galaxy center.

It predicts an increased branching ratio for pi0 -> e+e- decay.

The predicted decay enhancement matches recent experimental measurements.

Abstract

A model has been proposed in which neutral scalar particles chi, of mass 1-10 MeV, annihilate through the exchange of a light vector boson U, of mass 10-100 MeV, to produce the 511 keV line observed emanating from the center of the galaxy. The chi interacts weakly with normal matter and is a viable dark matter candidate. If the U-boson couples to quarks as well as to electrons, it could enhance the branching ratio for the rare decay pi0 -> e+e-. A recent measurement by the KTeV Collaboration lies three standard deviations above a prediction by Dorokhov and Ivanov, and we relate this excess to the couplings of the U-boson. The values are consistent with other constraints and considerations. We make some comments on possible improvements in the data.