The ATLAS detector data on di-lepton production is used in order to impose constraints on Z boson masses associated with a variety of 3-3-1 and E 6 motivated Z models. Lower mass bounds for the different models are established at 95% confidence level. Our numerical analysis is extrapolated up to 14 TeV, and further to 30 TeV and 100 TeV, for a broad range of luminosities. Some of our results can be compared with the ATLAS published bounds, being, for those cases, in fairly good agreement. We also report the vector and axial charges for all the 3-3-1-motivated Z models without exotic electric charges for leptons, known in the literature. To the best of our knowledge most of this charges were not reported before.

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By considering the 3-3-1 and the left-right symmetric models as low energy effective theories of the SU (3)C ⊗ SU (3)L ⊗ SU (3)R (for short [SU (3)] 3 ) gauge group, alternative versions of these models are found. The new neutral gauge bosons of the universal 3-3-1 model and its flipped versions are presented; also, the left-right symmetric model and its flipped variants are studied. Our analysis shows that there are two flipped versions of the universal 3-3-1 model, with the particularity that both of them have the same weak charges. For the left-right symmetric model we also found two flipped versions; one of them new in the literature which, unlike those of the 3-3-1, requires a dedicated study of its electroweak properties. For all the models analyzed, the couplings of the Z bosons to the standard model fermions are reported. The explicit form of the null space of the vector boson mass matrix for an arbitrary Higgs tensor and gauge group is also presented. In the general framework of the [SU (3)] 3 gauge group, and by using the LHC experimental results and EW precision data, limits on the Z mass and the mixing angle between Z and the new gauge bosons Z are obtained. The general results call for very small mixing angles in the range 10 −3 radians and M Z > 2.5 TeV.

A way of counting free parameters in the quark mass matrices of the standard model, including the constraints coming from weak basis transformations, is presented; this allow to understand the exact physical meaning of the parallel and non-parallel texture zeros which appear in some "ansätz" of the 3 × 3 quark mass matrices, including the CP violation phenomena in the analysis, it is shown why the six texture zeros are ruled out. Finally, a five texture zeros "ansätze"which properly copes with all experimental constrains, including the angles of the unitary triangle, is presented.

The phenomenology of the five independent sets of 3 × 3 quark mass matrices with five texture zeros is carried through in full detail, including predictions for the CP violation asymmetries. Our study is done without any approximation, first analytical and then numerical.

We report the most general expression for the chiral charges of a Z gauge boson coming from an E 6 unification model, as a function of the electroweak parameters and the charges of the U (1) factors in the chain of subgroups. These charges are valid for an arbitrary Higgs sector and only depend on the branching rules of the E 6 fundamental representation and the corresponding rules for the fermionic representations of their subgroups. By assuming E 6 unification, the renormalization group equations (RGE) allow us to calculate the electroweak parameters at low energies for most of the chains of subgroups in E 6 . From RGE and unitary conditions, we show that at low energies there must be a mixing between the gauge boson of the standard model hypercharge and the Z . From this, it is possible to delimit the preferred region in the parameter space for a breaking pattern in E 6 . In general, without unification, it is not viable to determine this region; however, for some models and under certain assumptions, it is possible to limit the corresponding parameter space. By using the most recent upper limits on the cross-section of extra gauge vector bosons Z decaying into dileptons from the ATLAS data at 13 TeV with accumulated luminosities of 36.1 fb −1 and 13.3 fb −1 , we report the 95% C.L. lower limits on the Z mass for the typical E 6 benchmark models. We also show the contours in the 95% C.L. of the Z mass bounds for the entire parameter space of E 6 .

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For a model with a fourth family of quarks, new sources of flavor changing neutral currents are identified by confronting the unitary 4 × 4 quark mixing matrix with the experimental measured values of the familiar 3×3 quark mixing matrix. By imposing as experimental constraints the known bounds for the flavor changing neutral currents, the largest mixing of the known quarks with the fourth family ones is established. The predictions are: a value for |V tb | significantly different from unity, large rates for rare top decays as t → cγ and t → cZ, the last one reachable at the Large Hadron Collider, and large rates for rare strange decays s → dγ and s → dg, where g stands for the gluon field.