Charged pion chain decay and the cosmic ray positron flux

Abstract

The study of the cosmic ray positron flux has attracted intense attention in recent years, especially because the observations suggest that it could receive contributions from sources such as pulsars or the self--annihilation or decay of dark matter particles. The main known source of relativistic positrons, that form the background to possible additional contributions, is the chain decay of $\pi^+$ produced in the inelastic interactions of cosmic rays with interstellar and circumstellar gas. The shape of the energy spectrum of positrons produced in these pion decays can be calculated exactly and is well known. However, surprisingly, some estimates of the contribution of the standard mechanism to the positron flux have adopted an incorrect spectral shape of the positron produced in these decays, following an error present in a 1997 paper of Moskalenko and Strong. In this work we report this error, discuss its origin, and estimate its impact on the numerical results.