A reduction in the UHE neutrino flux due to neutrino spin precession

Motivated by the stringent flux limits for UHE neutrinos coming from gamma ray bursts or active galactic nuclei, we explore the possibility that the active neutrinos generated in such astrophysical objects could oscillate to sterile right handed states due to a neutrino magnetic moment μν. We find that a value as small as μν≈10−15μB could produce such a transition thanks to the intense magnetic fields that are expected in these objects.