Decaying Dark Matter can explain the electron/positron excesses

TL;DR

Decaying dark matter can explain the PAMELA and ATIC electron-positron excesses without conflicting gamma-ray or radio observations. The analysis points to a TeV-scale DM particle with a long lifetime on the order of 10^26 seconds, decaying predominantly to leptons, with hadronic channels constrained by antiproton data. Unlike annihilating DM, decays avoid severe gamma-ray tensions for cuspy halos, and the authors outline observational tests, particularly via Galactic Ridge gamma rays. The work further provides a theoretical path linking DM to the baryon asymmetry through a technicolor-based, technibaryon scenario, offering a concrete mechanism to realize such DM and a natural explanation for the DM-to-baryon abundance ratio.

Abstract

PAMELA and ATIC recently reported excesses in e+ e- cosmic rays. Since the interpretation in terms of DM annihilations was found to be not easily compatible with constraints from photon observations, we consider the DM decay hypothesis and find that it can explain the e+ e- excesses compatibly with all constraints, and can be tested by dedicated HESS observations of the Galactic Ridge. ATIC data indicate a DM mass of about 2 TeV: this mass naturally implies the observed DM abundance relative to ordinary matter if DM is a quasi-stable composite particle with a baryon-like matter asymmetry. Technicolor naturally yields these type of candidates.

Figures (7)

• Figure 1: Left: The uncertain 'halo function' $I(\lambda_D)$ of eq. (\ref{['eq:fluxpositrons']}) that encodes the astrophysics of DM decays into positrons and their propagation 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 2: A fit of the DM decays indicated in the legend to the PAMELA positron data.
• Figure 3: Best-fit values of the DM life-time suggested by the PAMELA excess, for the DM decay modes indicated on the legend.
• Figure 4: Combined fit of positron data from PAMELA and of $e^++e^-$ data from ATIC, BBP-BETS, EC, HESS.
• Figure 5: Examples of fits of $e^+$ (left), $e^++e^-$ (center), $\bar{p}$ (right) CR data, for DM decay modes into $W^\pm \ell^\mp$ (that leads to an unseen $\bar{p}$ excess), $e^+e^-$ (that leads to a too sharp peak), $\tau^+\tau^-$ (that leads to peak less sharp than suggested by ATIC data). A combination of the last two possibilities, and the intermediate ${\rm DM}\to \mu^+\mu^-$ decay gives the optimal fit.