On Lepton Flavor Universality in Top Quark Decays

Abstract: We propose a novel strategy to test lepton flavor universality (LFU) in top decays, applicable to top pair production at colliders. Our proposal exploits information in kinematic distributions and mostly hinges on data-driven techniques, thus having very little dependence on our theoretical understanding of top pair production. Based on simplified models accommodating recent hints of LFU violation in charged current B meson decays, we show that existing LHC measurements already provide non-trivial information on the flavor structure and the mass scale of such new physics (NP). We also project that the measurements of LFU in top decays at the high-luminosity LHC could reach a precision at the percent level or below, improving the sensitivity to LFU violating NP in the top sector by more than an order of magnitude compared to existing approaches.