Quark–lepton universality and large leptonic mixing

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)SU(5) relation Md=MlT exists between the mass matrices of the down quarks and the charged leptons, and (iii) Md†=Md. These assumptions automatically lead to different mixing patterns for quarks and leptons: Quarks remain unmixed to leading order (i.e. VCKM=1VCKM=1) while leptons have non-trivial mixing given by a symmetric unitary matrix VPMNS0=VTV. V   depends on two physical mixing angles and for values of these angles ∼20°–25°∼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 VPMNS0. 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(VPMNS)e3>0.08.