A Couplet from Flavored Dark Matter

TL;DR

This paper proposes that lepton flavored dark matter models naturally produce a distinctive pair of closely spaced X-ray photon lines, which could explain recent observations like the 3.5 keV line.

Contribution

It introduces a model where dark matter flavors produce a photon couplet with energies determined by lepton masses, offering a novel explanation for observed X-ray lines.

Findings

Predicts a photon couplet in the keV-MeV range.

Line energy ratios are fixed by lepton masses.

Potential explanation for the 3.5 keV X-ray line.

Abstract

We show that a couplet, a pair of closely spaced photon lines, in the X-ray spectrum is a distinctive feature of lepton flavored dark matter models for which the mass spectrum is dictated by Minimal Flavor Violation. In such a scenario, mass splittings between different dark matter flavors are determined by Standard Model Yukawa couplings and can naturally be small, allowing all three flavors to be long-lived and contribute to the observed abundance. Then, in the presence of a tiny source of flavor violation, heavier dark matter flavors can decay via a dipole transition on cosmological timescales, giving rise to three photon lines. The ratios of the line energies are completely determined in terms of the charged lepton masses, and constitute a firm prediction of this framework. For dark matter masses of order the weak scale, the couplet lies in the keV-MeV region, with a much weaker line in the eV-keV region. This scenario constitutes a potential explanation for the recent claim of the observation of a 3.5 keV line. The next generation of X-ray telescopes may have the necessary resolution to resolve the double line structure of such a couplet.