Possible causes of a rise with energy of the cosmic ray positron fraction

TL;DR

The paper argues that the observed rise in cosmic ray positron fraction at energies above 7 GeV likely indicates a primary source of electron-positron pairs, dismissing alternative explanations as implausible.

Contribution

It provides a general, model-independent argument that a primary electron-positron source is necessary to explain the positron fraction rise in cosmic rays.

Findings

A primary source of electron-positron pairs is most likely responsible.

Alternative explanations are considered implausible.

Observational tests are proposed to distinguish scenarios.

Abstract

Based on general considerations rather than model-dependent fits to specific scenarios, we argue that an increase with energy of the positron fraction in cosmic rays, suggested by several experiments at E>~7 GeV, most likely requires a primary source of electron-positron pairs. We discuss the possible alternatives, and find none of them plausible on astrophysical or particle physics grounds. Further observational ways to test different scenarios are discussed.