Cosmic-Ray Positrons Strongly Constrain Leptophilic Dark Matter
  Cosmic-ray positrons have long been considered a powerful probe of dark
matter annihilation. In particular, myriad studies of the unexpected rise in
the positron fraction have debated its dark matter or pulsar origins. In this
paper, we instead examine the potential for extremely precise positron
measurements by AMS-02 to probe hard leptophilic dark matter candidates that do
not have spectral features similar to the bulk of the observed positron excess.
Utilizing a detailed cosmic-ray propagation model that includes a primary
positron flux generated by Galactic pulsars in addition to a secondary
component constrained by Helium and proton measurements, we produce a robust
fit to the local positron flux and spectrum. We find no evidence for a spectral
bump correlated with leptophilic dark matter, and set strong constraints on the
dark matter annihilation cross-section that fall below the thermal annihilation
cross-section for dark matter masses below 60 GeV and 380 GeV for annihilation
into $\tau^+\tau^-$ and $e^+e^-$, respectively, in our default model.
