Constraining the dark matter origin of the halo-like 20 GeV <i>γ</i> -ray excess with the AMS-02 antiproton data

Abstract Very recently, a significant ∼ 20 GeV gamma-ray excess in the Milky Way halo has been reported and a dark matter origin has been suggested. The inferred dark matter parameters are m χ ∼ 0.5–0.8 TeV and 〈 σv 〉 ∼ (5–8) × 10 -25 cm 3 s -1 for the bb̅ channel. If correct, prominent antiproton emission is produced and can be directly tested by the AMS-02 data. In this work we calculate the corresponding antiproton emission and show that the expected flux at ∼ 100 GeV is already above the AMS-02 observation. A proper treatment on the antiproton background resulting from the high energy cosmic ray propagation would suggest an annihilation cross section of < 2 × 10 -25 cm 3 s -1 , which is a few × 10 times lower than that needed to interpret the potential signal. We therefore conclude that the ∼ 20 GeV gamma-ray excess in the Milky Way halo is not a viable dark matter signal.