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

Abstract: 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. In addition, we present predictions within this interpretation for the positron fraction at higher energies for the antiproton flux, and discuss constraints from $\gamma$-ray measurements.