B Anomalies in Two Higgs Doublet Model with Flavor Symmetry

Abstract

The long-standing flavor anomalies in $b\to s{\ell }^{+}{\ell }^{-}$ and $b\to c\ell \hat{I}½$ persist. In this work, we explore a specific flavor-gauged two-Higgs doublet model (FG2HDM) extended by a scalar singlet, with an imposed $U(1)$ flavor symmetry. Compared to the Standard Model (SM), four additional scalars and one neutral gauge boson $Z^{\prime }$ are added to the particle spectrum. The special Yukawa coupling matrices, due to the $U(1)$ symmetry, lead to flavor-changing neutral Higgs (FCNH) interactions uniquely occurring in the down-type quark sector, while the new gauge boson $Z^{\prime }$ induces flavor-changing neutral current (FCNC) interactions in the down-type quark sector as well. The two distinct types of anomalies can be accommodated simultaneously in such a model. Incorporating scalar and vector contributions to $b\to s{\ell }^{+}{\ell }^{-}$ and $B_s^0$-${\bar{B}}_s^0$ mixing, along with charged Higgs contributions to $b\to c\ell \hat{I}½$, we investigate the parameter space in FG2HDM and find substantial room in the solution space. Specifically, in the SM-like model setup, the data suggests that $m_{Z^{\prime }}<450\text{GeV}$, $\tan {\hat{I}}^2<28$, and $g^{\prime }/m_{Z^{\prime }}>3.5\times 10^{-4}{\text{GeV}}^{-1}$, while there are fewer constraints on heavy scalars, which can be further tested by a combination of other observables.

32 pages, 4 figures for V1; 38 pages, 6 figures, the version accepted by PRD