The origin of the positron excess in cosmic rays

TL;DR

The paper explains the positron excess in cosmic rays as a natural result of secondary positron production within cosmic ray sources, where they are accelerated alongside primary particles, leading to a flat spectrum that matches observations.

Contribution

It demonstrates that the positron excess can be explained by secondary production and acceleration within supernova remnants, without invoking exotic sources.

Findings

Secondary positrons are produced and accelerated in the same region as cosmic rays.

Accelerated secondary positrons have a flat spectrum consistent with observations.

The effect's strength depends on environmental parameters during supernova remnant evolution.

Abstract

We show that the positron excess measured by the PAMELA experiment in the region between 10 and 100 GeV may well be a natural consequence of the standard scenario for the origin of Galactic cosmic rays. The 'excess' arises because of positrons created as secondary products of hadronic interactions inside the sources, but the crucial physical ingredient which leads to a natural explanation of the positron flux is the fact that the secondary production takes place in the same region where cosmic rays are being accelerated. Therefore secondary positrons (and electrons) participate in the acceleration process and turn out to have a very flat spectrum, which is responsible, after propagation in the Galaxy, for the observed positron 'excess'. This effect cannot be avoided though its strength depends on the values of the environmental parameters during the late stages of evolution of supernova remnants.