What could we learn from a sharply falling positron fraction?

TL;DR

This paper explores the implications of a potential sharp decline in the cosmic ray positron fraction, analyzing how such a feature could inform us about underlying sources like dark matter or pulsars.

Contribution

It investigates the consequences of a hypothetical sharp drop in the positron fraction, comparing pulsar and dark matter models in explaining this spectral feature.

Findings

Pulsar models can explain a sharp spectral cutoff as well as dark matter scenarios.

A steepening in the positron fraction would challenge existing secondary production models.

Future data showing a decline could help distinguish between different cosmic ray sources.

Abstract

Recent results from the AMS-02 data have confirmed that the cosmic ray positron fraction increases with energy between 10 and 200GeV. This quantity should not exceed 50%, and it is hence expected that it will either converge towards 50% or fall. We study the possibility that future data may show the positron fraction dropping down abruptly to the level expected with only secondary production, and forecast the implications of such a feature in term of possible injection mechanisms that include both dark matter and pulsars. {Were a sharp steepening to be found, rather surprisingly, we conclude that pulsar models would do at least as well as dark matter scenarios in terms of accounting for any spectral cut-off.