Reexamining the dark matter scenario accounting for the positron excess in a new cosmic ray propagation model

The positron excess in cosmic rays has stimulated a lot of interest in the last decade. The dark matter origin of the extra positrons has attracted great attention. However, the gamma-ray search set very stringent constraints on the dark matter annihilation/decay rate, which leads to great disfavor of the dark matter scenario. In this work, we incorporate the recent progress in cosmic ray propagation and reexamine the dark matter scenario accounting for the positron excess. Recent observations indicate that cosmic ray propagation in the Milky Way may be not uniform and diffusion in the Galactic disk should be slower than that in the halo. In the spatially dependent propagation model, the positrons/electrons are more concentrated in the disk and lead to smaller dark matter annihilation/decay rates to account for the positron excess and also a smaller deficit in the background positron flux. Especially for the mu thorn mu- channel the positron spectrum fits the AMS-02 latest data perfectly and the annihilation rate satisfies all the present constraints from gamma-ray and cosmic microwave background observations.