Bilepton and exotic quark mass limits in 331 models from Z → b b ¯ decay

We study the effect of new physics on the Z decay into bb pairs in the framework of 331 models. The decay Z{yields}bb is computed at one loop level and, using previous results, we evaluate this branching fraction in the framework of 331 models. A wide range of the space parameter of the model is considered and possible deviations from the standard model predictions are explored. From precision measurements at the Z pole we find the allowed region for the mass of exotic quarks M{sub J{sub 3}} and bileptons M{sub X} at 95% CL.