Galactic Center Radio Constraints on Gamma-Ray Lines from Dark Matter Annihilation

TL;DR

This paper investigates whether radio observations of the Galactic Center can confirm or refute gamma-ray line signals from dark matter annihilation, providing constraints on the annihilation cross section and dark matter profiles.

Contribution

It introduces a method to constrain dark matter annihilation to Zγ or Hγ using radio data, and assesses the robustness of these constraints under various assumptions.

Findings

Radio data marginally constrain the gamma-ray line interpretation for contracted NFW profiles.

Future radio telescopes can test annihilation cross sections as low as 10^{-28} cm^3 s^{-1}.

Constraints are robust across reasonable dark matter profile and magnetic field assumptions.

Abstract

Recent evidence for one or more gamma-ray lines at ~ 130 GeV in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to Z{\gamma} or H{\gamma} with an annihilation cross section, <\sigma v> ~ 10^{-27} cm^3 s^{-1} . We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from the decay of the Z or the H boson only in the Galactic Center against radio data from the same region in the Galactic Center. We find that the radio data from single dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes such as LWA, VLA-Low and LOFAR, and future radio telescopes like SKA, which are sensitive to annihilation cross sections as small as 10^{-28} cm^3 s^{-1}, can confirm or rule out this scenario very soon. We discuss the assumptions on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to Z{\gamma} or H{\gamma}.