Diphoton decay for a 750 GeV scalar boson in a SU (6)⊗ U (1) X model

Abstract

We propose a new SU (6) ⊗ U (1)X GUT model free from anomalies, with a 750 GeV scalar candidate which can decay into two photons, compatible with the recent diphoton signal reported by ATLAS and CMS collaborations. This model gives masses to all fermions and may explain the 750GeV signal through one loop decays to γγ with charged vector and charged Higgs bosons, as well as up-and electron-like exotic particles that arise naturally from the condition of cancellation of anomalies of the SU (6) ⊗ U (1)X group. We obtain, for different width approximations, allowed mass regions from 900 GeV to 3 TeV for the exotic up-like quark, in agreement with ATLAS and CMS collaborations data.Recently the ATLAS and CMS collaborations reported a diphoton signal excess with invariant mass of 750 GeV [1, 2] which has been the subject of many interpretations in the literature using different extensions of the standard model (SM) [3,4,5,6,7,8,9,10,11]. In this work, we consider the SU (6) ⊗ U (1) X extension proposed in [13] in the framework of the flipped SU (6) models [12] as a feasible model that may explain the diphoton excess. These kind of flipped models have very interesting features. First, by requiring a high breaking scale (∼ 10 17 GeV) for the flipped SU (6) and its SU (5) subgroup [14] the proton decay problem can be avoid. Second, they are able to solve the doublet-triplet splitting problem through the pseudo-Goldstone mechanism as in SU (6) [15,16] and [SU (3)] 3 [17]. Also, they provide unification of gauge couplings as in the flipped SU (5) model [18,19]. Finally, these models may develop see-saw masses compatible with the phenomenological active neutrinos [20,21] if one singlet heavy state is introduced.The SU (6) ⊗ U (1) X extension considered here contains the SU (3) C ⊗ SU (3) L ⊗ U (1) X model (hereafter 331 model) [22,23,24,25] as a subgroup that allow us address the observed diphoton excess through new exotic charged Higgs bosons into the loop at the TeV scale. In the flipped model, the U (1) X symmetry changes the exotic down type quark (charge −1/3) by an up type quark (charge 2/3) in the multiplets, which increases the coupling with photons and gluons into the loop, resulting in a significantly enhanced pp → γγ cross section, compatible with the reported data.The 331 model can be embedded into the grand unified group SU (6) ⊗ U (1) X with the following spontaneous symmetry breaking (SSB) chain:

Electroweak couplings and LHC constraints on alternative Z′ models in E6

“…A way to look for new models with a moderate fermion content is to consider alternative versions of the models already known in the literature. [1][2][3][4][5][6][7][8][9][10] Our work represents a first step in this direction. One of the first alternative models was "flipped SU (5)", 1,11 which produces a symmetry breaking for SO (10) down to SU (5) ⊗ U (1), where the U (1) factor contributes to the electric charge, and as such, its basic predictions for sin 2 θ W and the proton decay are known to be different from those of SU (5).…”

Lepton number violation in 331 models

“…These SU (3) C × SU (3) L × U (1) X (331) models have received considerable attention in connection with various topics: neutrino mass generation [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], flavour symmetries [32][33][34][35][36][37][38][39][40][41][42][43], quark flavour observables [44][45][46][47][48][49][50][51] or the recent LHC diphoton excess [52][53][54][55][56][57], among others. Underpinning this interest is the fact that the 331 to 321 symmetry breaking energy scale can be of the TeV order, hence it could possibly be explored at the LHC; see for example [58][59]…”