A Direct Constraint on Dimension-Eight Operators from Z-->neutrino   antinetrino gamma
  We study the radiative decay Z-->neutrino antineutrino gamma whitin 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 the dimension-six and the dimension-eight operators associated with the tau-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 the tau-neutrino magnetic moment. 
G. Tavares-Velasco, M. A. Perez, M. Maya and B. Vega