relation $f_0(0)=f_+(0)$. The situation is slightly less favorable in the case of $R_{D^\ast}$ since the needed form factors are not yet available from LQCD simulations at nonzero recoils. The strategy adopted is to extract the leading form factors from $B\to D^\ast l \bar{\nu}$, as explained in Sec. \[sec:Vcb\]. The remaining pseudoscalar form factor, $A_0(q^2)$, which cannot be extracted from data is then obtained by considerations based on HQET with generous error bars [@Bernlochner:2017jka; @Bigi:2017jbd]. The overall agreement in the literature is that the large departures from the SM cannot be explained by only relying on underestimated hadronic uncertainties. This conclusion is mostly based on the fact that the (unknown) $A_0(q^2)$ form factor gives a numerically small contribution to $R_{D^\ast}$ but still not negligible. It goes without saying that its computation on the lattice would be very welcome. Finally, it is worth mentioning that another potential source of uncertainty comes from the soft-photon radiation, which have been partially estimated in Ref. [@Becirevic:2009fy].

Effective field theory description {#sec:eft}
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In the following, we will assume that the $R_{D^{(\ast)}}$ anomalies are due to NP and we will discuss their implications. The transition $b\to c \ell \bar{\nu}$ (with $\ell=e,\mu,\tau$) can be generically described at 