Constraints on neutrino–photon interactions from rare Z decays

It is shown that the rare decays Z→νν̄γ and Z→νν̄γγ are useful to put model-independent bounds on neutrino–one-photon and neutrino–two-photon interactions. The results are then used to constrain the τ neutrino magnetic moment μντ and the double radiative decay νj→νiγγ. It is found that the decay Z→νν̄γ gives a more stringent bound on μντ than that obtained from Z→νν̄γγ; the latter decay in turn gives limits on the neutrino–two-photon interaction that are less stringent than those obtained for a sterile neutrino νs from the analysis of νμN→νsN conversion.