Unified Explanation of theeejj, Diboson, and Dijet Resonances at the LHC

Abstract

We show that the excess events observed in a number of recent LHC resonance searches can be simultaneously explained within a non-supersymmetric left-right inverse seesaw model for neutrino masses with WR mass around 1.9 TeV. The minimal particle content that leads to gauge coupling unification in this model predicts gR 0.51 at the TeV-scale, which is consistent with data. The extra color-singlet, SU (2)-triplet fermions required for unification can be interpreted as the Dark Matter of the Universe. Future measurements of the ratio of same-sign to opposite-sign dilepton events can provide a way to distinguish this scenario from the canonical cases of type-I and inverse seesaw, i.e. provide a measure of the relative magnitudes of the Dirac and Majorana masses of the right-handed neutrinos in the SU (2)R-doublet of the left-right symmetric model. INTRODUCTIONRecently, a number of resonance searches at the √ s = 8 TeV LHC have reported a handful of excess events around invariant mass of 1.8 -2 TeV. The most significant ones are: (i) a 3.4σ local (2.5σ global) excess in the ATLAS search [1] (see also [2] for the corresponding CMS searches reporting a mild excess at the same mass) for a heavy resonance decaying into a pair of Standard Model (SM) gauge bosons V V (with V = W, Z); (ii) a 2.8σ excess in the CMS search [3] for a heavy righthanded (RH) gauge boson W R decaying into an electron and RH neutrino N R , whose further decay gives an eejj final state; (iii) a 2.2σ excess in the CMS search [4] for W → W H, where the SM Higgs boson H decays into bb and W → ν (with = e, µ); (iv) a 2.1σ excess in the CMS dijet search [5]. These excesses of course need to be confirmed with more statistics at the LHC run II before any firm conclusion about their origin can be derived. Nevertheless, taking them as possible indications of new physics beyond the SM, it is worthwhile to examine whether all of them could be simultaneously explained within a self-consistent, ultra-violet complete theory that could be tested in foreseeable future.One class of models that seems to broadly fit the observed features in all the above-mentioned channels is the Left-Right Symmetric Model (LRSM) of weak interactions based on the gauge group SU (2) L × SU (2) R × U (1) B−L [6], with the RH charged gauge boson mass M W R ∼ 2 TeV and with g R < g L at the TeV-scale [7], g L(R) being the SU (2) L(R) gauge coupling strength. Within this framework, the eejj excess [3] can be understood [7][8][9][10] [7,13,14] in terms of W R → W Z, W H, since these couplings naturally arise in these models from the vacuum expectation values (VEVs) of the bidoublet field used to generate quark and lepton masses [6] (see [15] for some alternative explanations of the diboson excess). Finally, the dijet excess [5] can simply be due to W R → jj.However, a particular aspect of the observations in the eejj channel, namely, a suppression of same-sign electron pairs with respect to opposite-sign pairs [3], cannot be explained within the minimal LRSM with type-I seesaw mechanism....

Quasi-Dirac neutrinos at the LHC

“…Although we agree on the general statement, we find disagreement as concerns the dependence of R ll on the relevant model parameters. In particular, differently from [28], we find that the value of R ll does not display a parametric dependence on the overall right-handed (RH) neutrino mass scale. 5 Neutrino oscillation experiments have established that neutrino flavor numbers are not conserved.…”

Quasi-Dirac neutrinos at the LHC

“…Although we agree on the general statement, we find disagreement as concerns the dependence of R ll on the relevant model parameters. In particular, differently from [28], we find that the value of R ll does not display a parametric dependence on the overall right-handed (RH) neutrino mass scale. 5 Neutrino oscillation experiments have established that neutrino flavor numbers are not conserved.…”

Constraints on Z′ models from LHC dijet searches and implications for dark matter

“…We observe that rather weak bounds are obtained for m Z ≈ 1.6-1.7 TeV. The reason is that in this mass range all four experiments see an upward fluctuation in the data, so that the observed bound is weaker than the expected one (see also [42,43]). 5 Since we have consistently treated Γ and g q as independent parameters, our results can be applied to any Z model (with universal vector-like couplings to quarks) by applying the following procedure:…”

Testing the 2-TeV resonance with trileptons

“…For recent work which considers a similar model, see Ref. [6]. It is found that our model can actually realize the right number of eejj signals observed in the CMS experiment [1].…”

Quasi-Dirac neutrinos at the LHC

“…Although we agree on the general statement, we find disagreement as concerns the dependence of R ll on the relevant model parameters. In particular, differently from [28], we find that the value of R ll does not display a parametric dependence on the overall right-handed (RH) neutrino mass scale. 5 Neutrino oscillation experiments have established that neutrino flavor numbers are not conserved.…”

Constraints on Z′ models from LHC dijet searches and implications for dark matter

“…We observe that rather weak bounds are obtained for m Z ≈ 1.6-1.7 TeV. The reason is that in this mass range all four experiments see an upward fluctuation in the data, so that the observed bound is weaker than the expected one (see also [42,43]). 5 Since we have consistently treated Γ and g q as independent parameters, our results can be applied to any Z model (with universal vector-like couplings to quarks) by applying the following procedure:…”

Testing the 2-TeV resonance with trileptons

“…For recent work which considers a similar model, see Ref. [6]. It is found that our model can actually realize the right number of eejj signals observed in the CMS experiment [1].…”

Quasi-Dirac neutrinos at the LHC

“…Although we agree on the general statement, we find disagreement as concerns the dependence of R ll on the relevant model parameters. In particular, differently from [28], we find that the value of R ll does not display a parametric dependence on the overall right-handed (RH) neutrino mass scale. 5 Neutrino oscillation experiments have established that neutrino flavor numbers are not conserved.…”

Constraints on Z′ models from LHC dijet searches and implications for dark matter

“…We observe that rather weak bounds are obtained for m Z ≈ 1.6-1.7 TeV. The reason is that in this mass range all four experiments see an upward fluctuation in the data, so that the observed bound is weaker than the expected one (see also [42,43]). 5 Since we have consistently treated Γ and g q as independent parameters, our results can be applied to any Z model (with universal vector-like couplings to quarks) by applying the following procedure:…”

Testing the 2-TeV resonance with trileptons

“…For recent work which considers a similar model, see Ref. [6]. It is found that our model can actually realize the right number of eejj signals observed in the CMS experiment [1].…”