A direct constraint on dimension-eight operators from Z→νν̄γ

We study the radiative decay Z→νν̄γ within an effective Lagrangian approach. Using the search for energetic single-photon events in the data collected by the L3 Collaboration, we get direct bounds on dimension-six and dimension-eight operators associated with the τ-neutrino magnetic moment and the anomalous electromagnetic properties of the Z boson. As a by-product of our calculation, we reproduce the L3 result for the bound on μντ.