Bounds on mixing angles of fermions with their exotic partners using LEP 1990 data

Abstract

We have studied the bounds on mixing angles of fermions with their exotic partners which may stem from different possibilities of new physics. The tree level effects of mixing have been taken care of by a modification of the effective vector and axial-vector couplings of Z to the fermions. The radiative corrections arising from new physics of exotic fermions are assumed to be negligible; as a result the ρ parameter and the effective sin² θ_w are calculated within the framework of the Standard Model. Mixing angles have been treated as free parameters during simultaneous fits to the combined data of cross-sections and lepton asymmetries from the four LEP experiments which have collected over 550,000 Z⁰ decays in 1990. Fitted values of mixing angles and the upper bounds at 90% C. L. are discussed.