$R_K$ and $R_{K^{*}}$ in an aligned 2HDM with right-handed neutrinos

We consider the possibility of explaining the recent $R_K$ and $R_{K^{*}}$ anomalies in a two-Higgs doublet model, known as aligned, combined with a low-scale seesaw mechanism generating light neutrino masses and mixings. In this class of models, a large Yukawa coupling allows for significant nonuniversal leptonic contributions, through box diagrams mediated by charged Higgs bosons and right-handed neutrinos, to the $b\to s{\ell }^{+}{\ell }^{-}$ transition that can then account for both $R_K$ and $R_{K^{*}}$ anomalies.

Figure 1

The heavy neutrino contributions to the one-loop box diagrams of the $b\to s{\ell }^{+}{\ell }^{-}$ transition, with (a) two $W$ bosons, (b) one $W$ and one charged Higgs, and (c) two charged Higgs.

Figure 2

$\mathrm{BR}(\mu \to e\gamma )$ for $M_{H^{\pm }}=700\mathrm{GeV}$, $m_{{\nu }_{h_i}}=500\mathrm{GeV}$, $|(U_{Lh}{)}_{\mu i}{|}^2=0.4\times {10}^{-3}$, and ${\zeta }_{\ell }=0$. The dashed line corresponds to the MEG exclusion bound.

Figure 3

(a) $R_{K^{*}}$ in the central bin and (b) $\mathrm{BR}(B_s\to {\mu }^{+}{\mu }^{-})$ as a function of the combination of parameters that mostly controls the observable. The green bands are the $1\sigma$ and $2\sigma$ bands for the $R_{K^{*}}$ measurement. Blue (red) points correspond to the scenario in which the heavy neutrino has a non-negligible coupling only to the muon (electron) flavor eigenstates.

Figure 4

(a) Correlation between $R_{K^{*}}$ in the central and low bins. (b) Correlation between $R_{K^{*}}$ in the central bin and the predicted $\mathrm{BR}(B_s\to {\mu }^{+}{\mu }^{-})$. Here, only the $1\sigma$ bounds have been considered in both figures.