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Register a new userFlavor-changing neutral current in production and decay of pseudoscalar mesons in a type III two-Higgs-doublet-model with four-texture Yukawa couplings
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We study flavor violating processes in the production or decay of a neutral pseudoscalar meson $P^0$ in the framework of a general two Higgs Doublet Model type III (2HDM-III). We use a version of the model where Yukawa interactions of neutral Higgs bosons allow for flavor change at the tree-level, but conserves CP symmetry. We focus on all possible $tau^{pm} to l^{pm}P^0 $ and $P^0 to l^+l^-$ decay channels, where $l,l$ are charged leptons. We find that these processes provide complementary information on quark and lepton FCNC Yukawa couplings. In particular flavor violating parameters in the quark sector, $chi_{sb}$ and $chi_{db}$, are significantly constrained by present experimental data, whereas the corresponding parameters in the leptonic sector are less constrained.
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The new round of experiments, MEG II, COMET/Mu2e, and Mu3e, would soon start to push the $mu to egamma$, $mu N to eN$ conversion, and $mu to 3e$ frontier, while Belle II would probe $tau to mugamma$ and $tau to 3mu$. In the general two Higgs doublet model with extra Yukawa couplings, we show that all these processes probe the lepton flavor violating (LFV) dipole transition that arises from the two loop mechanism, with scalar-induced contact terms subdominant. This is because existing data suggest the extra Yukawa couplings $rho_{mu e},, rho_{ee} lesssim lambda_e$, while $rho_{taumu},, rho_{tautau} lesssim lambda_tau$ and $rho_{tt} lesssim lambda_t$, with $lambda_i$ the usual Yukawa coupling of the Standard Model (SM), where $rho_{mu e}rho_{tt}$ and $rho_{taumu}rho_{tt}$ enter the $mu egamma$ and $taumugamma$ two loop amplitudes, respectively. With the $B_s to mumu$ decay rate basically consistent with SM expectation, together with the $B_s$ mixing constraint, we show that $B_s to tautau$ would also be consistent with SM, while $B_s to taumu$ and $B to Ktaumu$ decays would be out of reach of projected sensitivities, in strong contrast with some models motivated by the B anomalies.
We propose a class of Two Higgs Doublet Models where there are Flavour Changing Neutral Currents (FCNC) at tree level, but under control due to the introduction of a discrete symmetry in the full Lagrangian. It is shown that in this class of models, one can have simultaneously FCNC in the up and down sectors, in contrast to the situation encountered in BGL models. The intensity of FCNC is analysed and it is shown that in this class of models one can respect all the strong constraints from experiment without unnatural fine-tuning. It is pointed out that the additional sources of flavour and CP violation are such that they can enhance significantly the generation of the Baryon Asymmetry of the Universe, with respect to the Standard Model.
With discovery of the 125 GeV boson $h^0$, the existence of a second doublet is very plausible. We show that the alignment phenomenon, that $h^0$ is found to resemble closely the Standard Model Higgs boson, may correspond to Higgs quartic couplings $eta_i$ that are ${cal O}(1)$ in strength. If the exotic bosons of the second doublet possess extra top Yukawa couplings, which are the least constrained by data, such a two Higgs doublet model could drive electroweak baryogenesis, as well as further protect the apparent alignment. The exotic Higgs bosons can be sub-TeV in mass while remaining well hidden so far, with broad parameter space for search at the Large Hadron Collider.
We analyse various flavour changing processes like $tto hu,hc$, $hto tau e,taumu$ as well as hadronic decays $hto bs,bd$, in the framework of a class of two Higgs doublet models where there are flavour changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely determined by the CKM and PMNS matrices as well as $tanbeta$. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalization group. We show that in some of the models the rates of the above flavour changing processes can reach the discovery level at the LHC at 13 TeV even taking into account the stringent bounds on low energy processes, in particular $muto egamma$.
With the deeper study of Higgs particle, Higgs precision measurements can be served to probe new physics indirectly. In many new physics models, vector-like quarks $T_L,~T_R$ occur naturally. It is important to probe their couplings with standard model particles. In this work, we consider the singlet $T_L,~T_R$ extended models and show how to constrain the $Tth$ couplings through the $hrightarrowgamma Z$ decay at high-luminosity LHC. Firstly, we derive the perturbative unitarity bounds on $|y_{L,~R}^{tT}|$ with other couplings set to be zeros simply. To optimize the situation, we take $m_T$ = 400 GeV and $s_L$ = 0.2 considering the experimental constraints. Under this benchmark point, we find that the future bounds from $hrightarrowgamma Z$ decay can limit the real parts of $y_{L,~R}^{tT}$ in the positive direction to be O(1) because of the double enhancement. For the real parts of $y_{L,~R}^{tT}$ in the negative direction, it is always surpassed by the perturbative unitarity. Moreover, we find that the top quark electric dipole moment can give stronger bounds (especially the imaginary parts of $y_{L,~R}^{tT}$) than the perturbative unitarity and $hrightarrowgamma Z$ decay in the off-axis regions for some scenarios.
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