$R_{D^{(\ast)}}$, $R_{K^{(\ast)}}$ and neutrino mass in the 2HDM-III with right-handed neutrinos

TL;DR

This paper proposes a unified 2HDM-III framework with right-handed neutrinos to simultaneously explain $R_{D^{(*)}}$, $R_{K^{(*)}}$ anomalies, and neutrino masses, predicting sub-eV neutrino masses and specific Wilson coefficients.

Contribution

It introduces a model embedding the low-scale type-I seesaw into 2HDM-III to address flavor anomalies and neutrino mass in a unified manner.

Findings

Addresses $R_{D^{(*)}}$ anomalies at 2σ level without violating $B_c$ decay bounds.

Predicts sub-eV neutrino masses with heavy Majorana neutrinos.

Generates the required Wilson coefficients for $R_{K^{(*)}}$ anomalies with $ ext{O}(1)$ Yukawa couplings.

Abstract

Given that the two-Higgs-doublet model of type III (2HDM-III) has the potential to address the $R_{D^{(\ast)}}$ anomalies while the resolution to the $R_{K^{(\ast)}}$ deficits requires new degrees of freedom within this framework, we consider in this paper a unified scenario where the low-scale type-I seesaw mechanism is embedded into the 2HDM-III, so as to accommodate the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies as well as the neutrino mass. We first revisit the $R_{D^{(\ast)}}$ anomalies and find that the current world-averaged results can be addressed at $2\sigma$ level without violating the bound from the branching ratio $\mathcal{B}(B_c^-\rightarrow \tau^- \bar{\nu})\leqslant 30\%$. The scenario predicts two sub-eV neutrino masses based on a decoupled heavy Majorana neutrino and two nearly degenerate Majorana neutrinos with mass around the electroweak scale. For the $R_{K^{(\ast)}}$ anomalies, the same scenario can generate the required Wilson coefficients in the direction $ C_{9 \mu}^{\rm NP}=-C_{10 \mu}^{\rm NP}<0$, with $\mathcal{O}(1)$ Yukawa couplings for the muon and the top quark.