Bounding the magnetic and electric dipole moments of tau nu from the   process e+e- --> nu bar nu gamma in E6 Superstring Models
  We obtain bounds on the anomalous magnetic and electric dipole moments of the tau-neutrino through the reaction $e^{+}e^{-}\to \nu \bar \nu \gamma$ at the $Z_1$-pole in the framework of a Left-Right symmetric model and a class of $E_6$ inspired models with an additional neutral vector boson $Z_\theta$. We use the data collected by the L3 Collaboration at LEP. For the parameters of the $E_6$ model we consider the mixing angle $\theta_{E_6}=37.8^o$ and $M_{Z_\theta}=7M_{Z_1}$. We find that our bounds are of the same order of magnitude as those obtained in other extensions of the Standard Model. 
A. Gutierrez-Rodriguez, M. A. Hernandez-Ruiz, B. Jayme-Valdes and M.   A. Perez