Constraining dark matter by the 511 keV line

TL;DR

This paper models dark matter annihilation near the Milky Way center, constraining possible channels and masses to explain the 511 keV positron line, gamma-ray, and positron excesses while considering the black hole's influence.

Contribution

It provides new constraints on dark matter annihilation channels and mass ranges consistent with multiple astrophysical observations, incorporating the effects of adiabatic contraction.

Findings

Only three annihilation channels fit the positron production and gamma-ray constraints.

The mu+ mu- channel mass range is approximately 80-100 GeV.

The scenario aligns with the density spike model near the supermassive black hole.

Abstract

In the past few decades, observations indicated that an unexplained high production rate of positrons (the strong 511 keV line) exists in the Milky Way center. By using the fact that a large amount of high density gas used to exist near the Milky Way center million years ago, we model the rate of positrons produced due to dark matter annihilation. We consider the effect of adiabatic contraction of dark matter density due to the supermassive black hole at the Milky Way center and perform a detailed calculation to constrain the possible annihilation channel and dark matter mass range. We find that only three annihilation channels ($\mu^+\mu^-$, $4e$ and $4 \mu$) can provide the required positron production rate and satisfy the stringent constraint of gamma-ray observations. In particular, the constrained mass range for the $\mu^+\mu^-$ channel is $m \approx 80-100$ GeV, which is close to the mass range obtained for the dark matter interpretation of the GeV gamma-ray and positron excess. In other words, the proposed scenario can simultaneously provide the required positron production rate to explain the 511 keV emission, the positron excess and the GeV gamma-ray excess in our Milky Way, and it is compatible with the density spike due to adiabatic growth model of the supermassive black hole.