Possible causes of a rise with energy of the cosmic ray positron fraction
Pasquale Dario Serpico
TL;DR
The rising cosmic-ray positron fraction at high energy poses a challenge to standard secondary production models. The paper adopts a model-independent, general-argument approach to evaluate possible explanations. It concludes that a primary source of high-energy $e^{+}e^{-}$ pairs is the most plausible origin, while other astrophysical or particle-physics scenarios are found unlikely. It also discusses observational tests to distinguish among scenarios and guide future measurements.
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.