Viability of detection by AMS of sudden features due to dark matter annihilation to positrons and electrons

TL;DR

This paper assesses the potential for AMS to detect dark matter annihilation signatures in cosmic ray spectra, concluding that such features are unlikely to be observable unless dark matter particles are lighter than about 40 GeV.

Contribution

It provides a calculation of expected spectral features from dark matter annihilation and compares them with existing measurements to evaluate detectability.

Findings

Spectral 'bumps' from dark matter annihilation are likely undetectable with AMS unless dark matter mass is below 40 GeV.

Current Fermi data already rules out prominent spectral features for annihilation cross sections around 10^{-26} cm^3/s.

Detection of such features requires dark matter particles to have relatively low mass, below approximately 40 GeV.

Abstract

The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [$\Phi_{e^+}/(\Phi_{e^+ + e^-})]$, and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to $e^+$ and $e^-$ final states. In this article, we calculate the signature "bumps" in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section $\sigma v \sim\, 10^{-26}$ cm$^3$/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than $\sim$40 GeV.