@Abdesselam:2016cgx]. When combined in the same fit, these results amount to a discrepancy with respect to the SM at the $\approx 4\,\sigma$ level [@Amhis:2016xyh]. This observation is corroborated by the first measurement of the ratio $R_{J/\Psi}=\mathcal{B}(B_c \to J/\Psi \tau \bar{\nu})/\mathcal{B}(B_c \to J/\Psi l \bar{\nu})$ [@Aaij:2017tyk], which also appears to be larger than the SM estimates [@RJpsipaper]. Another intriguing indication of LFU violation appeared in loop-induced processes,

$$\label{eq:RK-RKst}
R_{K^{(\ast)}} = \dfrac{\mathcal{B}(B\to K^{(\ast)} \mu\mu)}{\mathcal{B}(B\to K^{(\ast)}ee)}\Bigg{|}_{q^2\in [q^2_{\mathrm{min}},q^2_{\mathrm{max}}]}\,,$$

measured by LHCb in different $q^2$-bins below the $c\bar{c}$ resonances [@Aaij:2014ora; @Aaij:2017vbb]. The obtained values appear to be $\approx 2.5\,\sigma$ the SM predictions [@Hiller:2003js; @Bordone:2016gaq], amounting to a combined discrepancy at the $\approx 4\sigma$ level.

Both types of ratios are defined in such a way that the CKM matrix element dependence and most of the hadronic uncertainties cancel-out, which makes then rather clean observables. Therefore, if confirmed with more data, they will represent a very clear indication of NP.

In the following we will focus on two issues that recently attracted the attention of the theory community: (i) the extraction of $|V_{cb}|$ from $B\to D^\ast l \bar{\nu}$ decays, and (ii) the above-mentioned hints of LFU violation in charged-current processes. [^1]

Exclusive determinations of $|V_{cb}|$: latest developments 