The Price of a Dark Matter Annihilation Interpretation of AMS-02 Data

Understand

We discuss challenges to a dark matter annihilation interpretation of the excess positron fraction in the cosmic rays observed by the PAMELA, Fermi-LAT and AMS-02 collaborations.

• The spectra of positrons from annihilations into the leptonic two-body final states like $\tau^+ \tau^-$ or $\mu^+ \mu^-$, fit well the AMS-02 data for the positron ratio and the electron flux.
• Furthermore, we discuss the hadronic annihilation channels $b \bar{b}$ and $W^+ W^-$.
• However, this interpretation requires a very large annihilation cross section especially for the hadronic channels, conflicting with the unitarity upper limit, unless the positron flux due to annihilations is boosted by a large factor due to inhomogeneities in the galactic halo.