Excited Fermion Contribution to Z Physics at One Loop
  We investigate the effects induced by excited leptons at the one-loop level in the observables measured on the $Z$ peak at LEP. Using a general effective Lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to both oblique parameters and $Z$ partial widths. Our results show that the new effects are comparable to the present experimental sensitivity, but they do not lead to a significant improvement on the available constraints on the couplings and masses of these states. 
M.C.Gonzalez-Garcia (CERN-TH) and S.F. Novaes (IFT, Sao Paulo, Brasil)