Abstract
The study of anomalous electromagnetic emission in the sky is the basis of indirect searches for dark matter. It is also a powerful tool to constrain the radiative decay of active neutrinos. Until now, quantitative analyses have focused on the flux and energy spectrum of such an emission; polarisation has never been considered. Here we show that we could be missing out on an essential piece of information. The radiative decay of neutrinos, as well as the interactions of dark matter and neutrinos with Standard Model particles can generate a circular polarisation signal in X-rays or γ-rays. If observed, this could reveal important information about their spatial distribution and particle-antiparticle ratio, and could even reveal the nature of the high-energy particle physics processes taking place in astrophysical sites. The question of the observability of these polarised signatures and their separation from background astrophysical sources is left for future work.
Highlights
Nonzero neutrino masses and the existence of dark matter are two of the most robust indications that the Standard Model (SM) of particle physics is incomplete
Effect would single out the nature of the DM and the energy of the cosmic rays but it would enable to measure an asymmetry in the number density of dark matter and neutrinos
More work is needed to determine whether these signatures can lead to large enough signals to dominate potential circular polarisation emission from astrophysical background sources
Summary
Nonzero neutrino masses and the existence of dark matter are two of the most robust indications that the Standard Model (SM) of particle physics is incomplete. The circular polarisation of the radio spectrum is a clear indication of synchrotron emission and a powerful probe of the presence of high energy electrons [12, 13]. [14] it was suggested on the basis of symmetry considerations that the decay of asymmetric dark matter particles (such as sterile neutrinos) could induce circularly polarised X-ray line signals; Ref [15] showed that under certain conditions, dark matter annihilation via a charged mediator could give a net polarized state. The fraction of polarisation and the energy dependence of the polarised spectrum could be used to probe the existence of neutrino-electron interactions in astrophysical sites, as well as reveal dark matter interactions with ambient cosmic rays.
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