Dark Matter and Pulsar Origins of the Rising Cosmic Ray Positron Fraction in Light of New Data From AMS

TL;DR

This paper analyzes recent AMS data on cosmic ray positron fractions, exploring dark matter and pulsar origins, and finds certain dark matter models and pulsars remain viable explanations for the observed high-energy positrons.

Contribution

It reevaluates dark matter and pulsar models in light of new AMS measurements, identifying which scenarios can still explain the positron excess.

Findings

Some dark matter models are incompatible with new data.

Dark matter particles of 1-3 TeV annihilating to intermediate states remain plausible.

Nearby pulsars can still account for the positron fraction.

Abstract

The rise of the cosmic ray positron fraction with energy, as first observed with high confidence by PAMELA, implies that a large flux of high energy positrons has been recently (or is being currently) injected into the local volume of the Milky Way. With the new and much more precise measurement of the positron fraction recently provided by AMS, we revisit the question of the origin of these high energy positrons. We find that while some dark matter models (annihilating directly to electrons or muons) no longer appear to be capable of accommodating these data, other models in which ~1-3 TeV dark matter particles annihilate to unstable intermediate states could still be responsible for the observed signal. Nearby pulsars also remain capable of explaining the observed positron fraction. Future measurements of the positron fraction by AMS (using a larger data set), combined with their anticipated measurements of various cosmic ray secondary-to-primary ratios, may enable us to further discriminate between these remaining scenarios.