Right Unitarity Triangles, Stable CP-violating Phases and Approximate Quark-Lepton Complementarity

Abstract

Current experimental data indicate that two unitarity triangles of the CKM quark flavor mixing matrix V are almost the right triangles with \alpha \approx 90^\circ. We find that \alpha = 90^\circ actually points to {\rm Re}(V_{tb}V_{ud}V^*_{td}V^*_{ub}) = 0. Considering a very suggestive parametrization of V, we show that its CP-violating phase \phi is nearly equal to \alpha (i.e., \phi - \alpha \approx 1.1^\circ). Both \phi and \alpha are stable against the renormalizaton-group evolution from the electroweak scale M_Z to a superhigh energy scale M_X or vice versa, and thus it is impossible to obtain \alpha = 90^\circ at M_Z from \phi = 90^\circ at M_X. We conjecture that there might also exist a maximal CP-violating phase \phi \approx 90^\circ in the MNS lepton flavor mixing matrix U. The approximate quark-lepton complementarity relations, which hold in the standard parametrizations of V and U, can also hold in our particular parametrizations of V and U simply due to the smallness of |V_{ub}| and |V_{e3}|.