BOUNDS ON HEAVY CHIRAL FERMIONS

We derive the low-energy electroweak effective lagrangian for the case of additional heavy, unmixed, sequential fermions. Present data still allow for the presence of a new quark and/or lepton doublet with mass es greater than M(Z)/2, provided that these multiplets are sufficientl y degenerate, Deviations of the effective lagrangian predictions from a full one-loop computation are sizeable only for fermion masses close to the threshold M(Z)/2. Some of the constraints on new sequential fe rmions coming from accelerator results and cosmological considerations are presented, We point out that the new fermions can significantly a ffect the production and decay rate into gamma gamma of the intermedia te Higgs at LHC.