A dark matter model that reconciles tensions between the cosmic-ray $e^\pm$ excess and the gamma-ray and CMB constraints

TL;DR

This paper proposes a dark matter model using the Breit-Wigner mechanism with velocity-dependent annihilation cross sections to reconcile the cosmic-ray positron excess with gamma-ray and CMB constraints, fitting multiple observational data.

Contribution

It introduces a velocity-dependent annihilation cross section model that aligns the cosmic-ray excess explanation with gamma-ray and CMB limits, addressing previous tensions.

Findings

The model explains the AMS-02 positron excess without conflicting with gamma-ray constraints.

It achieves the correct relic density while satisfying observational bounds.

The velocity dependence suppresses annihilation signals in dwarf galaxies and during recombination.

Abstract

The cosmic-ray (CR) $e^\pm$ excess observed by AMS-02 can be explained by dark matter (DM) annihilation. However, the DM explanation requires a large annihilation cross section which is strongly disfavored by other observations, such as the Fermi-LAT gamma-ray observation of dwarf galaxies and the Planck observation of the cosmic microwave background (CMB). Moreover, the DM annihilation cross section required by the CR $e^\pm$ excess is also too large to generate the correct DM relic density with thermal production. In this work we use the Breit-Wigner mechanism with a velocity dependent DM annihilation cross section to reconcile these tensions. If DM particles accounting for the CR $e^\pm$ excess with $v\sim \mathcal{O}(10^{-3})$ are very close to a resonance in the physical pole case, their annihilation cross section in the Galaxy reaches a maximal value. On the other hand, the annihilation cross section would be suppressed for DM particles with smaller relative velocities in dwarf galaxies and at recombination, which may affect the gamma-ray and CMB observations, respectively. We find a proper parameter region that can simultaneously explain the AMS-02 results and the thermal relic density, while satisfying the Fermi-LAT and Planck constraints.