What Does The PAMELA Antiproton Spectrum Tell Us About Dark Matter?

TL;DR

This study revisits cosmic ray antiproton data to constrain dark matter properties, finding less stringent limits when accounting for propagation uncertainties and suggesting a possible dark matter origin for low-energy antiproton excess.

Contribution

It introduces a propagation model analysis that accounts for uncertainties, providing revised dark matter annihilation constraints and exploring the antiproton excess as a dark matter signal.

Findings

Propagation uncertainties weaken dark matter constraints.

Antiproton flux at low energies shows excess potentially from dark matter.

Best-fit dark matter parameters align with gamma-ray excess observations.

Abstract

Measurements of the cosmic ray antiproton spectrum can be used to search for contributions from annihilating dark matter and to constrain the dark matter annihilation cross section. Depending on the assumptions made regarding cosmic ray propagation in the Galaxy, such constraints can be quite stringent. We revisit this topic, utilizing a set of propagation models fit to the cosmic ray boron, carbon, oxygen and beryllium data. We derive upper limits on the dark matter annihilation cross section and find that when the cosmic ray propagation parameters are treated as nuisance parameters (as we argue is appropriate), the resulting limits are significantly less stringent than have been previously reported. We also note (as have several previous groups) that simple GALPROP-like diffusion-reacceleration models predict a spectrum of cosmic ray antiprotons that is in good agreement with PAMELA's observations above ~5 GeV, but that significantly underpredict the flux at lower energies. Although the complexity of modeling cosmic ray propagation at GeV-scale energies makes it difficult to determine the origin of this discrepancy, we consider the possibility that the excess antiprotons are the result of annihilating dark matter. Suggestively, we find that this excess is best fit for a dark matter mass of approximately 35 GeV and annihilation cross section of approximately 1e-26 cm^3/s (to b-bbar), in good agreement with the mass and cross section previously shown to be required to generate the gamma-ray excess observed from the Galactic Center.