Quark-Lepton universality and large leptonic mixing

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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 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=1) while leptons have non-trivial mixing given by a symmetric unitary matrix V⁰PMNS = Vᵗ V. 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 V⁰PMNS. We find that if the correction matrix equals the CKM matrix, the resulting lepton mixing agrees well with data and predicts θ₁₃ > 0.08. In a more general context, the assumption of partial universality (i.e., different mixing for the up and the down components of doublets) is shown to lead to a complementarity relation VPMNSVCKM=VᵗV in the lowest order.