Large electric dipole moments of heavy neutrinos

Abstract

In many models of CP violation, the electric dipole moment (EDM) of a heavy charged or neutral lepton could be very large. We present an explicit model in which a heavy neutrino EDM can be as large as $10^{-16}$ e-cm, or even a factor of ten larger if fine-tuning is allowed, and use an effective field theory argument to show that this result is fairly robust. We then look at the production cross section for these neutrinos, and by rederiving the Bethe-Block formula, show that they could leave an ionization track. It is then noted that the first signature of heavy neutrinos with a large EDM would come from $e^+e^-\to \bar{N}N\gamma$, leading to a very large rate for single photon plus missing energy events, and the rate and angular distribution are found. Finally, we look at some astrophysical consequences, including whether these neutrinos could constitute the UHE cosmic rays and whether their decays in the early universe could generate a net lepton asymmetry.