Electrons and Positrons in Cosmic Rays

TL;DR

This review summarizes recent findings on high-energy cosmic ray electrons and positrons, discussing anomalies, their possible origins, and emphasizing the need for high-resolution data to distinguish between models like pulsars and dark matter.

Contribution

It provides a systematic analysis of cosmic ray electron anomalies, compares models for their origin, and highlights the importance of high-resolution measurements for model discrimination.

Findings

Anomalies in electron and positron spectra observed in recent experiments.

High-resolution data may distinguish pulsar from dark matter origins.

Current data is insufficient to conclusively identify the source of anomalies.

Abstract

This review concentrates on the results obtained, over the last ten years, on the astrophysics of high-energy cosmic ray electrons and positrons. The anomalies, observed in the data of recent experiments (possible bump in the electron spectrum and the PAMELA anomaly in the positron fraction) are discussed through the systematic use of simple analytical solutions of the transport equations for cosmic ray electrons. Three main ways of explaining the origin of the anomalies are considered: the conservative way supposing the positrons to be pure secondary particles; the nearby sources like pulsars origin; and the dark matter origin. This review discusses, also, the inability to select the pulsars model or the dark matter model to explain the electron anomalies on the basis of the electron spectra with the usual large energy binning ($\gtrsim15%$). It is argued that the signature of nearby pulsars origin of the anomalies against the dark matter origin could be the fine structure of the cosmic ray electron spectrum predicted in the Malyshev et al. paper (2009) and which was observed in the data from the high-resolution ATIC experiment (2009-2011). To date, the high-resolution ATIC data was the only experimental result of this type published in the literature. Therefore, they should be tested by other experiments as soon as possible. Generally, there is, also, rather controversial situations between the data of the majority of recent experiments and, consequently, there is a noted urgent need for new high-precision and high-statistical experiments.