Signatures of leptophilic t-channel dark matter from active galactic nuclei

In this work, we study indirect photon signatures of leptophilic dark matter (DM) coming from Centaurus A (Cen A), where a DM density spike is believed to have survived to date contrary to the case of our galaxy. We consider a model where DM is a Majorana fermion which interacts with right-handed electrons via a scalar mediator. Assuming that the photons measured from the core of Cen A are coming from SM processes, we derive constraints on the average annihilation cross section which are 7 orders of magnitude stronger than the ones from measurements of the Galactic Center. Focusing on the allowed parameter space range, we calculate the flux of photons coming from the radiative DM-electron scattering in the active galactic nuclei (AGN) jets and the circular polarization asymmetry of these photons. We find that this flux is two orders of magnitude lower than the background but its circular polarization asymmetry can reach values close to 100%, indicating the need to experimentally exploit the high fraction of circular polarization in order to detect these interactions. Since the origin of the photons in the GeV-TeV range from Cen A is not completely clear and an exotic origin is compatible with the measurements as well, we also consider the scenario in which synchrotron radiation can only partially explain the photon flux and we fit the excess with signals coming from DM annihilation, finding a best fit for a DM candidate with a mass m???? = 123 GeV and a coupling aR = 0.018.

Automated summary

This work studies the indirect photon signatures of leptophilic dark matter from Centaurus A. The derived constraints on the average annihilation cross section are 7 orders of magnitude stronger than those from measurements of the Galactic Center. The study also explores the possibility of detecting these interactions by experimentally exploiting the high circular polarization asymmetry of the photons.