Minimal Dark Matter predictions for galactic positrons, anti-protons, photons

TL;DR

This work presents indirect-detection predictions for Minimal Dark Matter (MDM), focusing on three high-mass, electroweak multiplets and their Sommerfeld-enhanced annihilation channels into $W^+W^-$ and loop channels yielding photons, positrons, and antiprotons. The authors recompute production spectra with spin correlations using MadGraph and Pythia, then solve diffusion-loss equations for charged cosmic rays and model photon and synchrotron outputs across multiple halo profiles and propagation models, providing analytic fits and robust qualitative predictions. They find distinctive, high-energy signals at multi-TeV scales that rise above astrophysical backgrounds under reasonable boost factors and halo assumptions, with positron excesses already discussed in PAMELA data and promising prospects for AMS-02. The results offer concrete, testable benchmarks for upcoming cosmic-ray and gamma-ray observations, linking cosmological DM abundance to observable indirect-detection signatures using a highly predictive, parameter-free framework.

Abstract

We present the energy spectra of the fluxes of positrons, anti-protons and photons generated by Dark Matter annihilations in our galaxy, as univocally predicted by the model of Minimal Dark Matter. Due to multi-TeV masses and to the Sommerfeld enhancement of the annihilation cross section, distinctive signals are generated above the background, even with a modest astrophysical boost factor, in the range of energies soon to be explored by cosmic ray experiments.

Figures (7)

• Figure 1: Velocity dependence of Sommerfeld-enhanced MDM annihilation cross sections, for the two candidates that we mainly consider.
• Figure 2: Energy spectra of $e^+,\bar{p}, \gamma$ produced by non-relativistic ${\rm DM}\, {\rm DM}$ annihilations into SM vectors. Only $e^+$ have a secondary component (dashed green line shown on the $W^+W^-$ plot), that dominates at large $x\sim 1$.
• Figure 3: Photon flux from the galactic center for the isothermal (dashed, $\bar{J}=13.5$) and NFW (dotted, $\bar{J}=1380$) DM density profiles.
• Figure 4: Left: The uncertain 'halo function' $I(\lambda_D)$ of eq. (\ref{['eq:fluxpositrons']}) that encodes the astrophysics of DM DM annihilations into positrons and their propagation up to the Earth. The diffusion length is related to energy losses as in eq. (\ref{['eq:lambdaD']}). Right: The $\bar{p}$ astrophysical function $R(T)$ of eq. (\ref{['eq:RT']}), computed under different assumptions. In both cases, the dashed (solid) [dotted] bands assumes the min (med) [max] propagation configuration of eq. (\ref{['eq:proparampositrons']}) and eq. (\ref{['eq:proparam']}) respectively. Each band contains 3 lines, that correspond to the isothermal (red lower lines), NFW (blue middle lines) and Moore (green upper lines) DM density profiles.
• Figure 5: Positron fraction, $N_{e^+}/(N_{e^+}+N_{e^-})$, generated by ${\rm DM} \, {\rm DM}$ annihilations. The red (upper) curves refer to the 5-plet MDM candidate (eq.\ref{['sys:sample']}b). The blue (lower) ones to the 3-plet (eq.\ref{['sys:sample']}a). In the left plot we fix the NFW halo profile and vary the $e^+$ propagation model. In the right plot we fix the med propagation model and vary the DM halo profile. We assumed a boost factor $B=10$: notice that a signal above the background is present even for $B=1$, for the 5-plet case. The experimental data points are taken from HEATCAPRICEAMS01MASS.