Leptonic CP-violating asymmetry in e⁺e⁻ annihilation due to Z width effects

Abstract

CP-violating rate asymmetry can be generated in a process only if its amplitude possesses an absorptive part. Such an absorptive part can be provided in e⁺e⁻ annihilation by the presence of a Z resonance of nonzero width. The lepton-flavor-violating CP asymmetry in the process l_il̅_j(l̅_il_j), where l_i are charged leptons, is discussed in several models. In a specific two-Z model, with an extra U(1) gauge group corresponding to L_e-L_τ (L_e,L_τ being the lepton numbers associated with the electron and the τ lepton), large and observable CP asymmetry in e⁺e⁻→τ⁺e⁻(τ⁻e⁺) is shown to be possible at energies reached at the CERN e⁺e⁻ collider and SLAC Linear Collider. Various constraints coming from present experimental data have been taken into account while making this prediction.