Quark-lepton universality and large leptonic mixing

Abstract

A unified description of fermionic mixing is proposed which assumes that in certain basis (i) a single complex unitary matrix V diagonalizes mass matrices of all fermions to the leading order, (ii) the SU(5) relation M_d = M^τ_l exists between the mass matrices of the down quarks and the charged leptons, and (iii) M^†_d = M_d. These assumptions automatically lead to different mixing patterns for quarks and leptons: Quarks remain unmixed to leading order (i.e. VCKM=1) while leptons have non-trivial mixing given by a symmetric unitary matrix V⁰_PMNS=V^τV . V depends on two physical mixing angles and for values of these angles ˜20°-25° it reproduces the observed mixing patterns rather well. We identify conditions under which the universal mixing V follows from the universal mass matrices of fermions. Relatively small perturbations to the leading order structure lead to the CKM mixing and corrections to V⁰_PMNS. We find that if the correction matrix equals the CKM matrix, the resulting lepton mixing agrees well with data and predicts (VPMNS)_e3>0.08.