Importance of cosmic ray propagation on sub-GeV dark matter constraints

TL;DR

This paper investigates how cosmic ray propagation affects constraints on sub-GeV dark matter, showing that considering realistic propagation models significantly improves the limits from X-ray and gamma-ray observations, surpassing cosmological bounds.

Contribution

It demonstrates the importance of cosmic ray propagation modeling in deriving stronger astrophysical constraints on sub-GeV dark matter from X-ray and gamma-ray data.

Findings

Including cosmic ray propagation improves dark matter constraints from XMM-Newton.

Constraints exclude certain annihilation cross sections and decay lifetimes for 1 MeV to a few GeV DM.

Astrophysical bounds surpass cosmological limits across a wide mass range.

Abstract

We study sub-GeV dark matter (DM) particles that may annihilate or decay into SM particles producing an exotic injection component in the Milky Way that leaves an imprint in both photon and cosmic ray (CR) fluxes. Specifically, the DM particles may annihilate or decay into $e^+e^-$, $\mu^+\mu^-$ or $\pi^+\pi^-$ and may radiate photons through their $e^\pm$ products. The resulting $e^\pm$ products can be directly observed in probes such as {\sc Voyager 1}. Alternatively, the $e^\pm$ products may produce bremsstrahlung radiation and upscatter the low-energy galactic photon fields via the inverse Compton process generating a broad emission from $X$-ray to $\gamma$-ray energies observable in experiments such as {\sc Xmm-Newton}. We find that we get a significant improvement in the DM annihilation and decay constraints from {\sc Xmm-Newton} (excluding thermally averaged cross sections of $10^{-31}$ cm$^3$ s$^{-1} \lesssim \langle \sigma v\rangle \lesssim10^{-26}$ cm$^3$ s$^{-1}$ and decay lifetimes of $10^{26} \textrm{s}\lesssim \tau \lesssim 10^{28} \textrm{s}$ respectively) by including best fit CR propagation and diffusion parameters. This yields the strongest astrophysical constraints for this mass range of DM of 1 MeV to a few GeV and even surpasses cosmological bounds across a wide range of masses as well.