Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei

TL;DR

This paper investigates different astrophysical models explaining the PAMELA positron excess by analyzing cosmic ray nuclei data, supporting the hadronic source hypothesis over dark matter or pulsar explanations.

Contribution

It demonstrates how secondary cosmic ray nuclei measurements can distinguish between dark matter, pulsar, and hadronic models for positron excess.

Findings

Data supports hadronic cosmic ray sources for positron excess.

New titanium-to-iron ratio data aligns with hadronic models.

Predicted boron-to-carbon ratio at >100 GeV can test these models.

Abstract

The excess in the positron fraction reported by the PAMELA collaboration has been interpreted as due to annihilation or decay of dark matter in the Galaxy. More prosaically, it has been ascribed to direct production of positrons by nearby pulsars, or due to pion production during stochastic acceleration of hadronic cosmic rays in nearby sources. We point out that measurements of secondary nuclei produced by cosmic ray spallation can discriminate between these possibilities. New data on the titanium-to-iron ratio from the ATIC-2 experiment support the hadronic source model above and enable a prediction to be made for the boron-to-carbon ratio at energies above 100 GeV. Presently, all cosmic ray data are consistent with the positron excess being astrophysical in origin.