Lepton universality
= Lepton universality
{title2=$g_e=g_\mu=g_\tau$}
The <Standard Model> assigns the same <gauge coupling> to each lepton generation in the <weak charged current>. Different decay rates still arise from masses and phase space. Ratios of <leptonic pion decay> rates cancel the common hadronic decay constant and quark mixing coefficient, isolating universality and <helicity suppression>. Electromagnetic <radiative corrections> must be included for precision comparisons to inclusive measured decay rates.