Double beta decay, lepton flavor violation, and collider signatures of left-right symmetric models with spontaneousD-parity breaking

Abstract

We propose a class of left-right symmetric models (LRSMs) with spontaneous D parity breaking, where SU (2)R breaks at the TeV scale while discrete left-right symmetry breaks around 10 9 GeV. By embedding this framework in a non-supersymmetric SO(10) Grand Unified Theory (GUT) with Pati-Salam symmetry as the highest intermediate breaking step, we obtain gR/gL ≈ 0.6 between the right-and left-handed gauge couplings at the TeV scale. This leads to a suppression of beyond the Standard Model phenomena induced by the right-handed gauge coupling. Here we focus specifically on the consequences for neutrinoless double beta decay, low energy lepton flavour violation and LHC signatures due to the suppressed right handed currents. Interestingly, the reduced gR allows us to interpret an excess of events observed recently in the range of 1.9 TeV to 2.4 TeV by the CMS group at the LHC as the signature of a right handed gauge boson in LRSMs with spontaneous D parity breaking. Moreover, the reduced right-handed gauge coupling also strongly suppresses the non-standard contribution of heavy states to the neutrinoless double beta decay rate as well as the amplitude of low energy lepton flavour violating processes. In a dominant type-II Seesaw mechanism of neutrino mass generation, we find that both sets of observables provide stringent and complimentary bounds which make it challenging to observe the scenario at the LHC.

Neutrinos and collider physics

“…significant departure from SM expectations, the LHC data exhibit an intriguing excess in ee production with a local significance of 2.8σ for a candidate W R mass of M 2.1 W R ≈ TeV; no excess is observed in the μμ channel. The excess could be interpreted as a hint for W R production, but with a smaller RH gauge coupling g g 0.6 R L ≃ [329][330][331][332]. If the excess turns out to be statistically significant in future with more data and independent scrutiny from ATLAS, it might be an evidence for L-R symmetry with high-scale parity breaking [299].…”

Neutrinos and Collider Physics

“…The excess could be interpreted as a hint for W R production, but with a smaller RH gauge coupling g g 0.6 R L ≃ [329][330][331][332]. If the excess turns out to be statistically significant in future with more data and independent scrutiny from ATLAS, it might be an evidence for L-R symmetry with high-scale parity breaking [299].…”

The ATLAS diboson resonance in non-supersymmetric SO(10)

“…This case is potentially interesting since it may explain the 2.8σ anomaly observed by the CMS collaboration in the right-handed neutrino searches looking for dijet plus dilepton events [46]. Indeed, it turns out that W R with g 2R /g 2L 0.6 and m W R ∼ 2 TeV may explain the excess if the W R decays into a right-handed neutrino that mainly couples to first generation charged leptons [145][146][147], i.e. W ± R → ± N R → ± ± jj.…”