Double beta decay, lepton flavor violation, and collider signatures of left-right symmetric models with spontaneous<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>D</mml:mi></mml:math>-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 $1{0}^{9}\text{ }\text{ }\mathrm{GeV}$. By embedding this framework in a nonsupersymmetric $SO(10)$ grand unified theory (GUT) with Pati-Salam symmetry as the highest intermediate breaking step, we obtain ${g}_{R}/{g}_{L}\ensuremath{\approx}0.6$ 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 flavor violation, and LHC signatures due to the suppressed right handed currents. Interestingly, the reduced ${g}_{R}$ allows us to interpret an excess of events observed recently in the range of 1.9 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 nonstandard contribution of heavy states to the neutrinoless double beta decay rate as well as the amplitude of low-energy lepton flavor 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.