{#sec:Vcb}
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The CKM matrix element $|V_{cb}|$ is a free parameter of the SM that plays an important role in the unitarity triangle analysis and in the prediction of flavor changing neutral currents [@Charles:2015gya; @Bona:2006ah]. Its value is extracted by confronting the experimental results for the processes based on the transition $b\to c l\bar{\nu}$ with their SM predictions. Surprisingly, the values determined by using inclusive and exclusive $B$-meson decays show a discrepancy that only grew with time. The current averages quoted by HFLAV are [@Amhis:2016xyh] $$\begin{aligned}
 |V_{cb}|^{\mathrm{incl.}} &=(42.19\pm 0.78)\times 10^{-3}\,,\qquad\qquad\quad\qquad\qquad \text{from} \quad B\to X_c l \bar{\nu}\,,\\[0.3em]|V_{cb}|^{\mathrm{excl.}} &=(39.05\pm 0.47_{\mathrm{exp}}\pm 0.58_{\mathrm{th}})\times 10^{-3}\,, \qquad\quad\quad\hspace*{0.38em} \text{from} \quad B\to D^\ast l \bar{\nu}\,,\\[0.3em]
|V_{cb}|^{\mathrm{excl.}}  &=(39.18\pm 0.94_{\mathrm{exp}}\pm 0.36_{\mathrm{th}})\times 10^{-3}\,, \qquad\quad\quad\hspace*{0.38em} \text{from} \quad B\to D l \bar{\nu}\,,\end{aligned}$$ which differ by $\approx 3 \sigma$. To reliably extract these values it is crucial to control the hadronic uncertainties. [^2] While the relevant $B\to D$ form factors have been computed at nonzero recoil values by means of LQCD simulations [@Na:2015kha; @Lattice:2015rga], cf. discussion in Sec. \[sec:RD-sm\], some pieces of information on the $B\to D^\ast$ form factors are still lacking. The usual strategy in the latter case is to employ the overall form-factor normalization $[h_{A_1}(1)]$ computed on the lattice [@Bailey:2014tva; @Harrison:2016gup] and 