Abstract
We propose a model with two Higgs doublets and several SU(2) scalar singlets with a global non-Abelian flavor symmetry {mathcal{Q}}_6times {mathcal{Z}}_2 . This discrete group accounts for the observed pattern of fermion masses and mixing angles after spontaneous symmetry breaking. In this scenario only the third generation of fermions get their masses as in the Standard Model (SM). The masses of the remaining fermions are generated through a seesaw-like mechanism. To that end, the matter content of the model is enlarged by introducing electrically charged vector-like fermions (VLFs), right handed Majorana neutrinos and several SM scalar singlets. Here we study the processes involving VLFs that are within the reach of the Large Hadron Collider (LHC). We perform collider studies for vector-like leptons (VLLs) and vector-like quarks (VLQs), focusing on double production channels for both cases, while for VLLs single production topologies are also included. Utilizing genetic algorithms for neural network optimization, we determine the statistical significance for a hypothetical discovery at future LHC runs. In particular, we show that we can not safely exclude VLLs for masses greater than 200 GeV. For VLQ’s in our model, we show that we can probe their masses up to 3.8 TeV, if we take only into account the high-luminosity phase of the LHC. Considering Run-III luminosities, we can also exclude VLQs for masses up to 3.4 TeV. We also show how the model with predicted VLL masses accommodates the muon anomalous magnetic moment.
Highlights
Groups, containing one- and two-dimentional irreps, are [3]: S3, Q4, D4 and Q6.2 Both assumptions point to the idea on how to account for the three generations of quarks and leptons but not for their mass hierarchies
We propose a model with two Higgs doublets and several SU(2) scalar singlets with a global non-Abelian flavor symmetry Q6 × Z2
One fashionable approach to explain the fermion mass and mixing hierarchies is by using the Froggatt–Nielsen (FN) mechanism [14], where vector-like fermions (VLFs) are introduced to the Standard Model (SM) and transform under a new U(1)F symmetry which is spontaneously broken by the vevs of SU(2) scalar singlets
Summary
We propose a model where the SM gauge group is extended with a global flavor symmetry group, i.e. the complete description is given by the symmetry, SU(3)C × SU(2)L × U(1)Y × Q6 × Z2. Assuming that the right handed Majorana neutrinos have masses much larger than the electroweak symmetry breaking scale vEW = 246 GeV, the type I seesaw mechanism can be implemented to generate the tiny masses of the light active neutrinos. Notice that the flavon fields get decoupled when σi vEW or if one takes λ6,7,8,9 1 In this case, the CP-even parts of the SU(2) scalar doublets do not mix with the scalar singlets and their masses are obtained by diagonalizing the matrix. Scalar H1 is only coupled to the SM up-type sector and H2 to the down-type sector the Weinberg-Glasgow-Paschos theorem [17, 18] does not apply in this case, i.e. FCNCs might appear at tree-level due to the mixing between SM and vector like fermions We expect these FCNCs to be under control since they will be proportional to the small mixing angles and further suppressed by the square of the heavy non-SM scalar masses. A thorough analysis on this regard is out of the scope of this paper
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