While the detection of W R -boson at the Large Hadron Collider is likely to resolve the mystery of parity violation in weak interaction, observation of neutrinoless double beta decay (0νββ) is expected to determine whether neutrinos are Majorana fermions. In this work we consider a class of LR models with TeV scale W R , Z R bosons but having parity restoration at high scales where they originate from well known Pati-Salam symmetry or SO(10) grand unified theory minimally extended to accommodate inverse seesaw frame work for neutrino masses. Most dominant new contribution to neutrinoless double beta decay is noted to occur via W − L W − L mediation involving lighter sterile neutrino exchanges. The next dominant contribution is found to be through W − L W − R mediation involving both light and heavy right-handed neutrino or sterile neutrino exchanges. The quark-lepton symmetric origin of the computed value of the Dirac neutrino mass matrix is also found to play a crucial role in determining these and other results on lepton flavor violating branching ratios for τ → e + γ, τ → µ + γ, and µ → e + γ accessible to ongoing search experiments. The underlying non-unitarity matrix is found to manifest in substantial CPviolating effects even when the leptonic Dirac phase δ CP ≃ 0, π, 2π. Finally we explore a possible origin of the model in non-supersymmetric SO(10) grand unified theory where, in addition to low mass W ± R and Z R bosons accessible to Large Hadron Collider, the model is found to predict observable neutron-antineutron oscillation and lepto-quark gauge boson mediated rare kaon decay with Br (K L → µē) ≃ 10 −9 − 10 −11 .

Recently realization of TeV scale inverse seesaw mechanism in supersymmetric SO(10) framework has led to a number of experimentally verifiable predictions including low-mass W ± R and Z ′ gauge bosons and nonunitarity effects. Using nonsupersymmetric SO(10) grand unified theory, we show how a TeV scale inverse seesaw mechanism for neutrino masses is implemented with a low-mass Z ′ boson accessible to Large Hadron Collider. We derive renormalization group equations for fermion masses and mixings in the presence of the intermediate symmetries of the model and extract the Dirac neutrino mass matrix at the TeV scale from successful GUT-scale parameterization of fermion masses. We estimate leptonic nonunitarity effects measurable at neutrino factories and lepton flavor violating decays expected to be probed in near future. While our prediction on the nonunitarity matrix element ηµτ for degenerate right-handed neutrinos is similar to the supersymmetric SO(10) case, we find new predictions with significantly enhanced value of its phase δµτ ≃ 10 −4 − 10 −2 when partial degeneracy among these neutrino masses is adequately taken into account by a constraint relation that emerges naturally in this approach. Other predictions on branching ratios and CPviolating parameters are discussed. An important distinguishing characteristic as another test of the best identified minimal model is that the threshold corrected two-loop prediction on proton lifetime with maximum value (τp)max. ≃ 10 35 yrs. is accessible to ongoing search experiments for the decay p → e + π 0 . Simple model extensions with longer proton lifetime predictions are also discussed.

We discuss gauge coupling unification of SU(3) C × SU(2) L × U(1) Y descending directly from non-supersymmetric SO(10) while providing solutions to the three outstanding problems of the standard model: neutrino masses, dark matter, and the baryon asymmetry of the universe. Conservation of matter parity as gauged discrete symmetry for the stability and identification of dark matter in the model calls for high-scale spontaneous symmetry breaking through 126 H Higgs representation. This naturally leads to the hybrid seesaw formula for neutrino masses mediated by heavy scalar triplet and right-handed neutrinos. Being quadratic in the Majorana coupling, the seesaw formula predicts two distinct patterns of right-handed neutrino masses, one hierarchical and another not so hierarchical (or compact), when fitted with the neutrino oscillation data. Predictions of the baryon asymmetry via leptogenesis are investigated through the decays of both the patterns of RHν masses. A complete flavor analysis has been carried out to compute CP-asymmetries including washouts and solutions to Boltzmann equations have been utilised to predict the baryon asymmetry. The additional contribution to vertex correction mediated by the heavy left-handed triplet scalar is noted to contribute as dominantly as other Feynman diagrams. We have found successful predictions of the baryon asymmetry for both the patterns of right-handed neutrino masses. The SU(2) L triplet fermionic dark matter at the TeV scale carrying even matter parity is naturally embedded into the non-standard fermionic representation 45 F of SO(10). In addition to the triplet scalar and the triplet fermion, the model needs a nonstandard color octet fermion of mass ∼ 5 × 10 7 GeV to achieve precision gauge coupling unification at the GUT mass scale M 0 U = 10 15.56 GeV.Open Access, c The Authors. Article funded by SCOAP 3 .doi:10.1007/JHEP04(2017)075 JHEP04(2017)075Threshold corrections due to superheavy components of 126 H and other representations are estimated and found to be substantial. It is noted that the proton life time predicted by the model is accessible to the ongoing and planned experiments over a wide range of parameter space.

Proton decay and new contribution to 0ν2β decay in SO(10) with low-mass Z ′ boson, observable n −n oscillation, lepton flavor violation, and rare kaon decay Abstract:In the conventional approach to observable n −n oscillation through PatiSalam intermediate gauge symmetry in SO(10), the canonical seesaw mechanism is also constrained by the symmetry breaking scale M R ∼ M C ≤ 10 6 GeV which yields light neutrino masses several orders larger than the neutrino oscillation data. A method to evade this difficulty is through TeV scale gauged inverse seesaw mechanism which has been recently exploited while predicting experimentally verifiable W ± R , Z R bosons with a new dominant contribution to neutrinoless double beta decay in the W L −W L channel and other observable phenomena, but with proton lifetime far beyond the accessible limits. In the present work, adopting the view that W ± R may be heavy and currently inaccessible to accelerator tests, we show how a class of non-supersymmetric SO(10) models allows a TeV scale Z ′ boson, experimentally testable proton decay along with observable n −n oscillation, and leptoquark gauge boson mediated rare kaon decays without resorting to additional fine-tuning of parameters. The occurrence of Pati-Salam gauge symmetry with unbroken D-parity and two gauge couplings at the highest intermediate scale guarantees precision unification with vanishing GUT-threshold or gravitational corrections on sin 2 θ W (M Z ) prediction in this model. Predictions for neutrinoless double beta decay in the W L − W L channel is analysed in detail including light and heavy sterile neutrino exchange contributions by means of normal and band plots and also by scattered plots while a new formula for half-life is derived. Comparison with available data from various groups by normal and scattered plots reveals how the existing experimental bounds are satisfied irrespective of the mass JHEP01 (2015)045 hierarchy in the light neutrino sector leading to the lower bound on the lightest sterile neutrino mass,M S 1 ≥ 18 ± 2.9 GeV. The model also predicts branching ratios for charged lepton flavor violation verifiable by ongoing search experiments. We also derive new renormalisation group equations constraining the lepto-quark gauge boson mass in the presence of SU(2) L × U(1) R × U(1) B−L × SU(3) C symmetry, specific to the occurrence of extra Z ′ boson, leading to a new lower bound on the lepto-quark gauge boson mass mediating rare kaon decay, M LQ ≥ (1.54±0.06) × 10 6 GeV. We also discuss the symmetry breaking of non-SUSY SO(10) through the well known flipped SU(5) ×Ũ(1) path and show, for the first time, how TeV scale Z ′ is predicted with gauged inverse seesaw ansatz for neutrino masses and substantial lepton flavor and lepton number violations. As a significant new result along this path, we report a successful unification of the two gauge couplings of SU(5) ×Ũ(1) into the single GUT coupling of SO(10).

Inspired by the recent diboson excess observed at the LHC and possible interpretation within a TeV-scale Left-Right symmetric framework, we explore its implications for low-energy experiments searching for lepton number and flavor violation. Assuming a simple Type-II seesaw mechanism for neutrino masses, we show that for the right-handed (RH) gauge boson mass and coupling values required to explain the LHC anomalies, the RH contribution to the lepton number violating process of neutrinoless double beta decay (0νββ) is already constrained by current experiments for relatively low-mass (MeV-GeV) RH neutrinos. The future ton-scale 0νββ experiments could probe most of the remaining parameter space, irrespective of the neutrino mass hierarchy and uncertainties in the oscillation parameters and nuclear matrix elements. On the other hand, the RH contribution to the lepton flavor violating process of µ → eγ is constrained for relatively heavier (TeV) RH neutrinos, thus providing a complementary probe of the model. Finally, a measurement of the absolute light neutrino mass scale from future precision cosmology could make this scenario completely testable.Introduction-A number of recent resonance searches with the √ s = 8 TeV LHC data have observed excess events around an invariant mass of 2 TeV. The most conspicuous one is a 3.4σ local excess in the AT-LAS search [1] for a heavy resonance decaying into a pair of Standard Model (SM) gauge bosons V V (with V = W, Z), followed by the hadronic decay of the diboson system. The corresponding CMS search also reports a mild excess around the same mass [2]. In addition, the CMS searches have reported a 2.2σ excess in the W H channel (H being the SM Higgs boson) [3], a 2.1σ excess in the dijet channel [4] and a 2.8σ excess in the eejj channel [5], all around the same invariant mass of 2 TeV. Of course, these excesses should be thoroughly scrutinized in light of possible subtleties in the analysis [6] and must be confirmed with more statistics at the LHC run II before a firm conclusion on their origin could be deduced. Nevertheless, given the lucrative possibility that it could easily be the first glimpse of new physics at the LHC, it seems worthwhile to speculate on some well-motivated beyond SM interpretations.