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

TL;DR

This paper reexamines the dark matter explanation for the cosmic ray positron excess using a new spatial-dependent propagation model, which better fits observational data and constraints from gamma-ray and CMB measurements.

Contribution

It introduces a spatial-dependent cosmic ray propagation model that reduces the required dark matter annihilation rate to explain the positron excess.

Findings

The new model fits AMS-02 positron data well for the bcm channel.

Dark matter annihilation rate is lower and consistent with gamma-ray and CMB constraints.

Positron excess can be explained without conflicting with existing observational limits.

Abstract

The positron excess in cosmic rays has stimulated a lot of interests 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 the work, we incorporate the recent progress in cosmic rays propagation and reexamine the dark matter scenario accounting for the positron excess. Recent observations indicate that cosmic rays 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 spatial-dependent propagation model, the positrons/electrons are more concentrated in the disk and lead to smaller dark matter annihilation/decay rate to account for the positron excess and also a smaller deficit in the background positron flux. Especially for the $\mu^+\mu^-$ channel the positron spectrum fit the AMS-02 latest data perfectly and the annihilation rate satisfies all the present constraints from $\gamma$-ray and CMB observations.