Universal lepton universality violation in exclusive processes

In high energy exclusive processes involving leptons, QED corrections can be sensitive to infrared scales like the lepton mass and soft photon cut, resulting in large logarithms that need resummed all order $\ensuremath{\alpha}$. When considering ratio of between two different flavors, $R$ expressed terms factorized functions decoupled leptonic sectors. While some functional cancel, there remain due difference cut. This factorization process universally applied such as $Z\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{l}$, where result gives significant deviations from naive expectation universality.