Antiproton and Positron Signal Enhancement in Dark Matter Mini-Spikes Scenarios

TL;DR

This work investigates antimatter signals from dark matter annihilation in a population of mini-spikes around intermediate-mass black holes. It develops a statistical framework to compute the boost factor $B$ and its variance by sampling the number, positions, and annihilation volumes of mini-spikes, linking the signal to the Green-function propagator and the annihilation volume through $\varphi_i=S\,G(\mathbf{x}_i)\,\xi_i$ with $\xi_i=B_i M_i/\rho_0$. The authors find very large mean boosts (up to $\sim 10^4$ for positrons and antiprotons) but with energy-dependent, long-tailed variances that differ between positrons and antiprotons due to distinct propagation physics; these results imply that mass inferences from positron cut-offs could be biased and that the presence of substructures can dramatically alter indirect-detection signals. The study emphasizes that correlating multiple antimatter channels and incorporating realistic substructure distributions are essential for robust DM constraints with upcoming experiments like PAMELA and AMS-02.

Abstract

The annihilation of dark matter (DM) in the Galaxy could produce specific imprints on the spectra of antimatter species in Galactic cosmic rays, which could be detected by upcoming experiments such as PAMELA and AMS02. Recent studies show that the presence of substructures can enhance the annihilation signal by a "boost factor" that not only depends on energy, but that is intrinsically a statistical property of the distribution of DM substructures inside the Milky Way. We investigate a scenario in which substructures consist of $\sim 100$ "mini-spikes" around intermediate-mass black holes. Focusing on primary positrons and antiprotons, we find large boost factors, up to a few thousand, that exhibit a large variance at high energy in the case of positrons and at low energy in the case of antiprotons. As a consequence, an estimate of the DM particle mass based on the observed cut-off in the positron spectrum could lead to a substantial underestimate of its actual value.

Figures (9)

• Figure 1: Distribution of the Monte-Carlo realizations of the galactic mini-spike population -- extracted from Ref. Bertone:2005xz -- as a function of the number $N_{\rm BH}$ of objects within a galactocentric radius of 100 kpc.
• Figure 2: Schematic representation of the inner structure of a mini-spike
• Figure 3: The probability law $q(\xi)$ for the annihilation volume has been derived from the Monte-Carlo results of Ref. Bertone:2005xz. We found no correlation with the mini-spike position.
• Figure 4: Radial distribution of the mini-spikes, as extracted from the numerical results of Ref. Bertone:2005xz.
• Figure 5: Results from the Monte-Carlo simulations of the IMBHs population inside the Milky Way are compared to the analytical computations of the effective boost factor and its dispersion, for $m_{\chi} = 1 \; {\rm TeV}$.