Cosmic-Ray Positrons Strongly Constrain Leptophilic Dark Matter

TL;DR

Precise measurements of cosmic-ray positrons by AMS-02 strongly limit the parameter space of leptophilic dark matter, especially for masses below 60 GeV and 380 GeV, with no spectral evidence supporting dark matter origins.

Contribution

This study uses detailed cosmic-ray propagation modeling and AMS-02 data to set new constraints on leptophilic dark matter, improving upon previous limits by accounting for pulsar contributions.

Findings

No spectral bump indicative of leptophilic dark matter detected.

Constraints on dark matter annihilation cross-section are below thermal relic levels for certain masses.

Limits are particularly strong for dark matter masses below 60 GeV and 380 GeV.

Abstract

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.