Cosmic-ray deuteron excess from a primary component

TL;DR

This paper investigates the excess of cosmic-ray deuterons observed by AMS-02, demonstrating that a primary component is necessary and proposing a new fusion process at CR sources to explain the data.

Contribution

It introduces a revised calculation of secondary deuteron flux and proposes a novel primary deuteron production mechanism via fusion at CR sources.

Findings

Updated cross sections reduce the need for primary deuterons

A primary deuteron component is still required to match observations

Fusion at CR sources can produce primary deuterons naturally

Abstract

The recent AMS-02 measurements of cosmic-ray (CR) deuteron fluxes suggest the presence of primary deuterons in quantities far exceeding predictions from Big Bang nucleosynthesis. This poses a significant challenge to modern astrophysics, as no known processes can account for such large amounts of deuterons without violating existing constraints~\cite{Epstein:1976hq}. In contrast, it is recently proposed that the AMS-02 measurements can be explained by a purely secondary origin when contributions from heavier nuclei are considered. In this study, we recalculate the secondary deuteron flux using production cross sections updated with the latest collider data. We find that some of the deuteron production cross sections are overestimated in the widely-used calculation tools for CR propagation, and a primary deuteron component is still necessary. We then propose a novel process for generating primary deuterons at CR sources through a fusion mechanism, which is naturally unique to deuterons. This model could explain the observed deuteron excess while maintaining consistency with other CR measurements.