Ruling Out Spiky WIMP Dark Matter using Indirect Searches

TL;DR

This paper uses gamma-ray and neutrino observations to place new constraints on the existence and steepness of dark matter density spikes near the Galactic Center, challenging the presence of such spikes for WIMP dark matter.

Contribution

It provides the first comprehensive bounds on the spike profile slope using indirect detection data, considering a generic WIMP scenario with fixed annihilation cross-section.

Findings

Constraints exclude steep DM spikes for WIMP masses 10 GeV to 100 TeV.

Even a 1% photon channel contribution is ruled out for certain spike profiles.

IceCube data constrains steep spikes in the 1-10 TeV mass range.

Abstract

The dark matter (DM) density profile in the innermost region of the Galaxy remains an open question. In particular, while adiabatic growth of the supermassive black hole Sgr A$^\ast$ at the Galactic Center (GC) can induce a 'spike' in central DM density, the existence of such a spike is still under debate. Here we present new constraints on the spike slope $\gamma_{\rm sp}$ using conventional DM indirect detection searches. We first recast existing photon and neutrino line searches, which include the contribution from the GC region, into constraints on the thermally-averaged DM annihilation cross section $\langle\sigma v\rangle$ in the presence of a DM spike. We then derive new bounds on the spike profile for a generic Weakly Interacting Massive Particle (WIMP) DM scenario, where the thermal freeze-out mechanism fixes the annihilation cross-section at $\langle\sigma v\rangle\sim (2-3) \times 10^{-26}~{\rm cm}^3~{\rm s}^{-1}$. We find that for DM annihilation to photons, constraints from Fermi-LAT and MAGIC rule out spike profiles at the GC for a broad range of WIMP DM masses from 10 GeV to 100 TeV. Our result holds even if the photon channel constitutes only $1\%$ of the total annihilation rate. For the neutrino channel, we use the IceCube data to constrain the existence of an extremely steep spike in the $\mathscr{O}(1-10)$ TeV DM mass range. Our analysis can be easily extended to other annihilation channels.