The most recent measurements of the observables $R_{D^{(*)}}$ are in tension with the Standard Model offering hints of New Physics in $brightarrow c ell bar{ u}_{ell}$ transitions. Motivated by these results, in this work we present an analysis on their $brightarrow u ell bar{ u}_{ell}$ counterparts (for $ell=e, ~mu, ~tau$). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic $B$ decays ($B^-rightarrow ell^- bar{ u}_{ell}$, $bar{B}rightarrow pi ell bar{ u}_{ell}$ and $bar{B}rightarrow rho ell bar{ u}_{ell}$). Here a key role is played by the leptonic $B$ processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel $B^-rightarrow mu^-bar{ u}_{mu}$ by the Belle collaboration. Secondly, we extract the CKM matrix element $|V_{ub}|$ while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic $B$ decays.
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