| Izvleček: | Abstract Motivated by a dynamical enhancement of the electromagnetic corrections by a power of ΛQCD/m b in B d,s → μ + μ − at next-to-leading order (NLO), we extend the QED factorization effects on the leptonic B meson decays with light muon leptons to tauonic final states, B d,s → τ + τ − , using soft-collinear effective theory (SCET). This extension is necessary owing to the appearance of the large τ mass, which will lead to different power counting in SCET and also different results. We provide a complete NLO electromagnetic corrections to B d,s → τ + τ − , which include hard functions and hard-collinear functions below the bottom quark mass scale μ b . The power enhanced electromagnetic effects from hard-collinear contributions on B d,s → μ + μ − discussed before also exist in B d,s → τ + τ − . However the logarithm term arising from contributions of hard-collinear photon and lepton virtualities for B d,s → τ + τ − is not large as it is in muon case due to the hard-collinear scale of τ mass, which lead to only approximately 0.04% QED corrections to the branching fraction of B d,s → τ + τ − compared with overall reduction about 0.5% in B d,s → μ + μ − .
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