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Register a new userSuppression of scalar mediated FCNCs in a $SU(3)_ctimes SU(3)_Ltimes U(1)_X$-model
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The models based on $SU(3)_Ctimes SU(3)_Ltimes U(1)_X$ gauge symmetry (331-models) have been advocated to explain the number of fermion families. These models place one quark family to a different representation than the other two. The traditional 331-models are plagued by scalar mediated quark flavour changing neutral currents (FCNC) at tree-level. So far there has been no concrete mechanisms to suppress these FCNCs in 331-models. Recently it has been shown that the Froggatt-Nielsen mechanism can be incorporated into the 331-setting in an economical fashion (FN331-model). The FN331-model explains both the number of fermion families in nature and their mass hierarchy simultaneously. In this work we study the Higgs mediated quark FCNCs in FN331-model. The flavour violating couplings of quarks are suppressed by the ratio of the $SU(2)_L times U(1)_Y$ and $SU(3)_Ltimes U(1)_X$ breaking scales. We find that the $SU(3)_Ltimes U(1)_X$-breaking scale can be as low as 5 TeV in order to pass the flavour bounds.
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The models with the gauge group $SU(3)_ctimes SU(3)_L times U(1)_X$ (331-models) have been advocated to explain why there are three fermion generations in Nature. As such they can provide partial understanding of the flavour sector. The hierarchy of Yukawa-couplings in the Standard Model is another puzzle which remains without compelling explanation. We propose to use Froggatt-Nielsen -mechanism in a 331-model to explain both fundamental problems. It turns out that no additional representations in the scalar sector are needed to take care of this. The traditional 331-models predict scalar flavour changing neutral currents at tree-level. We show that they are strongly suppressed in our model.
We study the left-right asymmetric model based on SU(3)_C otimes SU(2)_L otimes SU(3)_R otimes U(1)_X gauge group, which improves the theoretical and phenomenological aspects of the known left-right symmetric model. This new gauge symmetry yields that the fermion generation number is three, and the tree-level flavor-changing neutral currents arise in both gauge and scalar sectors. Also, it can provide the observed neutrino masses as well as dark matter automatically. Further, we investigate the mass spectrum of the gauge and scalar fields. All the gauge interactions of the fermions and scalars are derived. We examine the tree-level contributions of the new neutral vector, Z_R, and new neutral scalar, H_2, to flavor-violating neutral meson mixings, say K-bar{K}, B_d-bar{B}_d, and B_s-bar{B}_s, which strongly constrain the new physics scale as well as the elements of the right-handed quark mixing matrices. The bounds for the new physics scale are in agreement with those coming from the rho-parameter as well as the mixing parameters between W, Z bosons and new gauge bosons.
Massive neutrino is an evidence of new physics beyond the Standard Model. One of the well motivated new physics scenarios is a model with gauged lepton flavor symmetry. We investigate neutrino properties in the minimal SU$(3)_elltimes$SU$(3)_E$ gauged lepton flavor model. In this model, three new species of fermions are introduced to cancel gauge anomalies. These new fermions lead to a see-saw mechanism for neutrino mass generation. We impose the constraints from perturbative unitarity in 2-2 scattering processes, as well as current experimental constraints, to obtain viable neutrino spectrum. We determine the lower bound, with the SU(3)$_ell$ gauge coupling set to 1, on the lightest neutrino mass of $3.76times10^{-3},(18.9times10^{-3}),$ eV for the normal (inverted) hierarchy.
The Standard Model prediction for $epsilon/epsilon$ based on recent lattice QCD results exhibits a tension with the experimental data. We solve this tension through $W_R^+$ gauge boson exchange in the $SU(2)_Ltimes SU(2)_Rtimes U(1)_{B-L}$ model with `charge symmetry, whose theoretical motivation is to attribute the chiral structure of the Standard Model to the spontaneous breaking of $SU(2)_Rtimes U(1)_{B-L}$ gauge group and charge symmetry. We show that $M_{W_R}<58$ TeV is required to account for the $epsilon/epsilon$ anomaly in this model. Next, we make a prediction for the neutron EDM in the same model and study a correlation between $epsilon/epsilon$ and the neutron EDM. We confirm that the model can solve the $epsilon/epsilon$ anomaly without conflicting the current bound on the neutron EDM, and further reveal that almost all parameter regions in which the $epsilon/epsilon$ anomaly is explained will be covered by future neutron EDM searches, which leads us to anticipate the discovery of the neutron EDM.
The Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix and flavor-changing neutral currents (FCNCs) in the quark sector are examined in the GUT inspired $SO(5) times U(1) times SU(3)$ gauge-Higgs unification in which the 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Gauge invariant brane interactions play an important role for the flavor mixing in the charged-current weak interactions. The CKM matrix is reproduced except that the up quark mass needs to be larger than the observed one. FCNCs are naturally suppressed as a consequence of the gauge invariance, with a factor of order $10^{-6}$. It is also shown that induced flavor-changing Yukawa couplings are extremely small.
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