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