Fermi-LAT kills dark matter interpretations of AMS-02 data. Or not?

TL;DR

This paper examines whether dark matter explanations for the positron anomaly are compatible with gamma-ray observations, proposing a dark matter disk model to reconcile the data.

Contribution

It introduces a dark matter disk model that alleviates conflicts between positron excess explanations and gamma-ray constraints from Fermi-LAT.

Findings

Standard dark matter models conflict with gamma-ray background measurements.

A dark matter disk can reduce gamma-ray signals, easing observational tensions.

Proposed models suggest a thin dark matter disk could explain cosmic ray data without contradicting gamma-ray observations.

Abstract

A number of papers attempt to explain the positron anomaly in cosmic rays, observed by PAMELA and AMS-02, in terms of dark matter (DM) decays or annihilations. However, the recent progress in cosmic gamma-ray studies challenges these attempts. Indeed, as we show, any rational DM model explaining the positron anomaly abundantly produces final state radiation and Inverse Compton gamma rays, which inevitably leads to a contradiction with Fermi-LAT isotropic diffuse gamma-ray background measurements. Furthermore, the Fermi-LAT observation of Milky Way dwarf satellites, supposed to be rich in DM, revealed no significant signal in gamma rays. We propose a generic approach in which the major contribution to cosmic rays comes from the dark matter disc and prove that the tension between the DM origin of the positron anomaly and the cosmic gamma-ray observations can be relieved. We consider both a simple model, in which DM decay/annihilate into charged leptons, and a model-independent minimal case of particle production, and we estimate the optimal thickness of DM disk. Possible mechanisms of formation and its properties are briefly discussed.