Flavor phenomenology of an extended 2HDM with inverse seesaw mechanism

TL;DR

This paper explores flavor physics in an extended 2HDM with inverse seesaw, analyzing leptonic and quark sector observables, and finds most new physics effects are below current experimental limits.

Contribution

It provides a comprehensive analysis of flavor observables in an extended 2HDM with inverse seesaw, including new constraints and predictions for rare decays and FCNC processes.

Findings

Leptonic LFV decays depend on Higgs couplings to exotic leptons.

Most FCNC processes are below experimental bounds.

Top quark FCNC processes are within current experimental limits.

Abstract

We perform a detailed and comprehensive study of several flavor physics observables in both lepton and quark sectors within the framework of an extended 2HDM theory where the inverse seesaw mechanism is implemented to generate the SM fermion mass hierarchy. In that theory, the SM gauge symmetry is supplemented by the local $U(1)_X$ and discrete $Z_4\times Z_2$ groups. In particular, we find that the leptonic flavor observables specifically, the branching ratios of LFV decays $\mu\to e\gamma, \tau\to e(\mu)\gamma$ and the anomalous magnetic moments $\Delta a_{e(\mu)}$ strongly depend on the couplings of the neutral CP even(odd) Higgses with exotic charged lepton $E_1$, whereas other observables involving BR($l\to 3l'$), Mu-$\overline{\text{Mu}}$ transition and coherent conversion $\mu \to e $ in a muonic atom are predicted to be less than several orders of magnitude compared to the corresponding experimental limits. Regarding the quark sector, the most stringent limits arising from the FCNC process involving the down-type quark $d_a\to d_b$ ($a=1,2,3$) transitions such as BR($\bar{B}\to X_s \gamma$), BR$(B_s\to \mu^+\mu^-)$, and meson mixing $ \Delta m_{K,B_s, B_d}$. Considering the obtained constraints from these observables, the new physics contributions to other observables namely BR$(B_s\to \tau^+\mu^-)$, BR$(B^+\to K^+\tau^+\tau^-)$, BR$(B^+\to K^+\tau^+\mu^-)$, and FCCC $b\to c$ transition LFUV ratios $R_{D^{(*)}}$ are shown to be remarkably small. Regarding the observables in the up-type quark transitions, the FCNC top quark processes $t\to u(c)\gamma$ and $t\to u(c)h$ have branching ratios consistent with the experimental limits. Additionally, observables related to SM-like Higgs boson decays BR$(h\to \bar{l}'l)$ and modified couplings $a_{h\bar{f}f}$ are also discussed.