Standard Model predictions for Lepton Flavour Universality ratios of inclusive semileptonic $B$ decays

Abstract

We present Standard Model predictions for lepton flavour universality ratios of inclusive $B\to X_{(c)} \ell \bar\nu_\ell$. For the $\ell=\mu,e$, these ratios are very close to unity as expected. For the $\tau$ mode, we update the SM prediction for the branching ratio including power-corrections in the heavy-quark expansion up to $1/m_b^3$. These inclusive ratios serve as an important cross-check of the exclusive $B\to D^{(*)}\ell\bar\nu_\ell$ modes, in which tensions exists between the predictions and measurements in those modes.