Cosmic-ray cooling by dark matter in astrophysical jets

Astrophysical jets from powerful active galactic nuclei (AGN) have recently been proposed as promising probes of dark matter (DM) in the sub-GeV mass range. AGN launch relativistic jets that accelerate cosmic rays (CRs) to very high energies, which can then interact with their surroundings and produce multiwavelength (MW) emission spanning from radio frequencies to TeV $\gamma$ rays. If DM consists of light particles, their interactions with CRs could lead to an additional cooling mechanism that modifies the expected MW emission. In this work, we analyse the MW spectrum of Markarian 421, a well-studied AGN, using a multizone leptonic jet model that includes the interactions between CR electrons and DM particles. For the first time, we account for the uncertainties in the astrophysical jet dynamics, which have been previously neglected when constraining the CR-DM interactions. By fitting simultaneously jet parameters and DM-electrons interactions, we use the MW data from \mkn to set constraints on the DM-induced CR cooling. We obtain 5$\sigma$ upper limit $\sigma_\text{DM-e} \lesssim 1 \times 10^{-34}~\text{cm}^2$ for a DM mass of $1~{\rm MeV}$. We demonstrate that this is about a factor of 2--10 stronger than traditional approaches depending on DM mass. This improvement originates from having indeed considered the full multi-wavelength emission from the source, instead if a simplified approach. Properly accounting for degeneracies between jet dynamics and DM interactions is also key to deriving robust constraints on DM interactions.