Neutrino Trident Production: A Powerful Probe of New Physics with   Neutrino Beams
  The production of a mu+mu- pair from the scattering of a muon-neutrino off the Coulomb field of a nucleus, known as neutrino trident production, is a sub-weak process that has been observed in only a couple of experiments. As such, we show that it constitutes an exquisitely sensitive probe in the search for new neutral currents among leptons, putting the strongest constraints on well-motivated and well-hidden extensions of the Standard Model gauge group, including the one coupled to the difference of the lepton number between the muon and tau flavor, L_mu-L_tau. The new gauge boson, Z', increases the rate of neutrino trident production by inducing additional $(\bar\mu \gamma_\alpha \mu)(\bar\nu \gamma^\alpha \nu)$ interactions, which interfere constructively with the Standard Model contribution. Existing experimental results put significant restrictions on the parameter space of any model coupled to muon number L_mu, and disfavor a putative resolution to the muon g-2 discrepancy via the loop of Z' for any mass m_Z' > 400 MeV. The reach to the models' parameter space can be widened with future searches of the trident production at high-intensity neutrino facilities such as the LBNE. 
Wolfgang Altmannshofer, Stefania Gori, Maxim Pospelov, Itay Yavin
hep-ph hep-ex