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Radiative Corrections to the Solar Lepton Mixing Sum Rule

The simple correlation among three lepton flavor mixing angles $(θ^{}_{12}, θ^{}_{13}, θ^{}_{23})$ and the leptonic Dirac CP-violating phase $δ$ is conventionally called a sum rule of lepton flavor mixing, which may be derived from a class of neutrino mass models with flavor symmetries. In this paper, we consider the solar lepton mixing sum rule $θ^{}_{12} \approx θ^ν_{12} + θ^{}_{13} \cos δ$, where $θ^ν_{12}$ stems from a constant mixing pattern in the neutrino sector and takes the value of $θ^ν_{12} = 45^\circ$ for the bi-maximal mixing (BM), $θ^ν_{12} = \tan^{-1}(1/\sqrt{2}) \approx 35.3^\circ$ for the tri-bimaximal mixing (TBM) or $θ^ν_{12} = \tan^{-1}\left[2/(\sqrt{5} + 1)\right] \approx 31.7^\circ$ for the golden-ratio mixing (GR), and investigate the renormalization-group (RG) running effects on lepton flavor mixing parameters when this sum rule is assumed at a superhigh-energy scale. For illustration, we work within the framework of the minimal supersymmetric standard model (MSSM), and implement the Bayesian approach to explore the posterior distribution of $δ$ at the low-energy scale, which becomes quite broad when the RG running effects are significant. Moreover, we also discuss the compatibility of the above three mixing scenarios with current neutrino oscillation data, and observe that radiative corrections can increase such a compatibility for the BM scenario, resulting in a weaker preference for the TBM and GR ones.