Rephasing Invariant Formula for CP Phase in Kobayashi-Maskawa Parametrization and Exact Sum Rule with Unitarity Triangle $δ_{\rm PDG} + δ_{\rm KM} = π- α+ γ$

In this letter, we obtain a rephasing invariant formula for the CP phase in the Kobayashi--Maskawa parameterization $δ_{\rm KM} = \arg [ - { V_{ud} \det V_{\rm CKM} / V_{us} V_{ub} V_{cd} V_{td}} ]$. General perturbative expansion of the formula and observed value $δ_{\rm KM} \simeq π/2$ reveal that the phase difference of the 1-2 mixings $e^{i (ρ_{12}^{d} - ρ_{12}^{u})}$ is close to maximal for sufficiently small 1-3 quark mixings $s_{13}^{u,d}$. Moreover, combining this result with another formula for the CP phase $δ_{\rm PDG}$ in the PDG parameterization, we derived an exact sum rule $δ_{\rm PDG} + δ_{\rm KM} = π- α+ γ$ which relating the phases and the angles $α, β, γ$ of the unitarity triangle.