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MeV Dark Matter: Has It Been Detected?

Celine Boehm, Dan Hooper, Joseph Silk, Michel Casse

TL;DR

This work evaluates whether the 511 keV gamma-ray line from the galactic bulge can arise from annihilating MeV-scale dark matter into e+e−. It combines INTEGRAL spatial data with DM halo models, annihilation cross sections, and relic-density calculations to show consistency under certain velocity dependences and mediator scenarios. The analysis highlights two viable paths: MeV DM with a light mediator yielding velocity-suppressed cross sections, and heavier (~100 MeV) DM with a roughly velocity-independent cross section, both compatible with current astrophysical and particle-physics constraints. The study also discusses observable implications of these models, including potential signals of a light U-boson and the prospects for future tests.

Abstract

We discuss the possibility that the recent detection of 511 keV gamma-rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (~MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.

MeV Dark Matter: Has It Been Detected?

TL;DR

This work evaluates whether the 511 keV gamma-ray line from the galactic bulge can arise from annihilating MeV-scale dark matter into e+e−. It combines INTEGRAL spatial data with DM halo models, annihilation cross sections, and relic-density calculations to show consistency under certain velocity dependences and mediator scenarios. The analysis highlights two viable paths: MeV DM with a light mediator yielding velocity-suppressed cross sections, and heavier (~100 MeV) DM with a roughly velocity-independent cross section, both compatible with current astrophysical and particle-physics constraints. The study also discusses observable implications of these models, including potential signals of a light U-boson and the prospects for future tests.

Abstract

We discuss the possibility that the recent detection of 511 keV gamma-rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (~MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.

Paper Structure

This paper contains 10 sections, 7 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Positron Propagation and Annihilation
  3. The Dark Matter Halo Profile
  4. The Annihilation Cross Section
  5. Relic Density and Astrophysical Constraints
  6. Relic Density
  7. Astrophysical Constraints
  8. Assessment
  9. Possible Models And Particle Physics Constraints
  10. Conclusions

Figures (1)

  • Figure 1: The angular distribution of $\gamma$-rays from DM annihilation averaged over the $2^{\circ}$ angular resolution of the SPI spectrometer on INTEGRAL for several halo profiles. SPI's observation indicates a full width half maximum of $9^{\circ}$ with a $6^{\circ}-18^{\circ}$ 2$\sigma$ confidence interval. Shown as vertical dashed and dotted lines are the central value and 2$\sigma$ limits of the angular widths found by SPI. To agree with this data, a halo model with $\gamma \sim$ 0.4-0.8 is favored.