Limits on excited tau leptons masses from leptonic tau decays
  We study the effects induced by excited leptons on the leptonic tau decay at one loop level. Using a general effective lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to the leptonic decays and use the current experimental values of the branching ratios to put limits on the mass of excited states and the substructure scale. 
J. I. Aranda, R. Martinez and O. A. Sampayo