Multi-messenger constraints on dark matter annihilation into electron-positron pairs

TL;DR

This study combines multi-wavelength astronomical data to set constraints on dark matter annihilation into electron-positron pairs, limiting the annihilation cross-section and the density profile of the Milky Way's dark matter halo.

Contribution

It provides new upper limits on dark matter annihilation cross-section and the Milky Way's halo density profile based on combined observational data.

Findings

Dark matter annihilation cross-section must be below the thermal relic value for masses under a few GeV.

Inner density slope of the Milky Way halo is constrained to be less than 1 to 1.5 depending on dark matter mass.

Steeper density profiles are incompatible with lighter thermal relic dark matter.

Abstract

We investigate the production of electrons and positrons in the Milky Way within the context of dark matter annihilation. Upper limits on the relevant cross-section are obtained by combining observational data at different wavelengths (from Haslam, WMAP, and Fermi all-sky intensity maps) with recent measurements of the electron and positron spectra in the solar neighbourhood by PAMELA, Fermi, and HESS. We consider synchrotron emission in the radio and microwave bands, as well as inverse Compton scattering and final-state radiation at gamma-ray energies. According to our results, the dark matter annihilation cross-section into electron-positron pairs should not be higher than the canonical value for a thermal relic if the mass of the dark matter candidate is smaller than a few GeV. In addition, we also derive a stringent upper limit on the inner logarithmic slope, alpha, of the density profile of the Milky Way dark matter halo (alpha < 1 if m_dm < 5 GeV, alpha < 1.3 if m_dm < 100 GeV and alpha < 1.5 if m_dm < 2 TeV) assuming that cross-section = 3 x 10^(-26) cm^3 s(-1). A logarithmic slope steeper than alpha about 1.5 is hardly compatible with a thermal relic lighter than about 1 TeV, regardless of the dominant annihilation channel.