Hint of a new scalar interaction in LHCb data?

We explain recent LHCb measurements of the lepton universality ratios, $R_{D^{(\ast )}}^{\tau \mathrm{/}\mathrm{\ell }}\equiv \frac{\mathcal{B}(\bar{B}\to D^{(\ast )+}{\tau }^{-}{\bar{\nu }}_{\tau })}{\mathcal{B}(\bar{B}\to D^{(\ast )+}{\mathrm{\ell }}^{-}{\bar{\nu }}_{\mathrm{\ell }})}$ and ${R({\mathrm{\Lambda }}_c^{+})}^{\tau \mathrm{/}\mathrm{\ell }}\equiv \frac{\mathcal{B}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\tau }^{-}{\bar{\nu }}_{\tau })}{\mathcal{B}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\ell }}^{-}{\bar{\nu }}_{\mathrm{\ell }})}$ with $\mathrm{\ell }=\mu$, via new physics that affects $R_D^{\tau \mathrm{/}\mathrm{\ell }}$ and $R({\mathrm{\Lambda }}_c^{+}{)}^{\tau \mathrm{/}\mathrm{\ell }}$ but not $R_{D^{\ast }}^{\tau \mathrm{/}\mathrm{\ell }}$. The scalar operator in the effective theory for new physics is indicated. We find that the forward-backward asymmetry and $\tau$ polarization in $\bar{B}\to D^{+}{\tau }^{-}{\bar{\nu }}_{\tau }$ and ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\tau }^{-}{\bar{\nu }}_{\tau }$ decays are significantly affected by the scalar interaction. We construct a simple two Higgs doublet model as a realization of our scenario and consider lepton universality in semileptonic charm and top decays, radiative $B$ decay, $B$-mixing, and $Z\to b\bar{b}$.