Antiprotons from Dark Matter: Effects of a Position-Dependent Diffusion Coefficient

TL;DR

This paper investigates how a position-dependent diffusion coefficient affects the predicted antiproton flux from dark matter, revealing significant deviations from traditional models that assume a constant diffusion coefficient.

Contribution

It introduces an extended model with an exponentially increasing diffusion coefficient and includes contributions from the entire dark matter halo, improving upon conventional approaches.

Findings

Antiproton flux can differ by up to 25% from traditional models.

Including the full dark matter halo significantly impacts flux predictions.

A new analytic approximation for flux with position-dependent diffusion is provided.

Abstract

Energetic antiprotons in cosmic rays can serve as an important indirect signature of dark matter. Conventionally, the antiproton flux from dark matter decays or annihilations is calculated by solving the transport equation with a space-independent diffusion coefficient within the diffusion zone of the galaxy, and assuming free propagation outside this zone. Antiproton sources outside of the diffusion zone are ignored. In reality, it is far more likely that the diffusion coefficient increases smoothly with distance from the disk, and the outlying part of the dark matter halo ignored in the conventional approach can be significant, containing as much as 90% of the galactic dark matter by mass in some models. We extend the conventional approach to address these issues. We obtain analytic approximations and numerical solutions for antiproton flux assuming that the diffusion coefficient increases exponentially with the distance from the disk, and including contributions from dark matter annihilations/decays in essentially the full dark matter halo. We find that the antiproton flux predicted in this model deviates from the conventional calculation for the same dark matter parameters by up to about 25%.