Abstract
We assess the sensitivity of the LHC, its high energy upgrade, and a prospective 100 TeV hadronic collider to the Dirac Yukawa coupling of the heavy neutrinos in left-right symmetric models (LRSMs). We focus specifically on the trilepton final state in regions of parameter space yielding prompt decays of the right-handed gauge bosons ($W_R$) and neutrinos ($N_R$). In the minimal LRSM, the Dirac Yukawa couplings are completely fixed in terms of the mass matrices for the heavy and light neutrinos. In this case, the trilepton signal provides a direct probe of the Dirac mass term for a fixed $W_R$ and $N_R$ mass. We find that while it is possible to discover the $W_R$ at the LHC, probing the Dirac Yukawa couplings will require a 100 TeV $pp$ collider. We also show that the observation of the trilepton signal at the LHC would indicate the presence of a non-minimal LRSM scenario.
Highlights
Soon after the appearance of the original works [1,2,3], the minimal left-right symmetric model has been proposed to connect the smallness of neutrino masses with the spontaneous violation of parity [4,5,6]
We show that the observation of the trilepton signal at the LHC would indicate the presence of a nonminimal left-right symmetric models (LRSMs) scenario
The high value of the transverse momentum cut on the lepton in Table I is still useful to suppress the events coming from the ordinary W boson decay, though we are not be able to confirm the existence of the WR if there is an excess observed in the experiment. (iii) The typical mass of the lightest heavy neutrino is O(100) GeV in our study unlike Refs. [21,38] with Oð10Þ GeV heavy neutrinos (HNs) masses
Summary
Soon after the appearance of the original works [1,2,3], the minimal left-right symmetric model (mLRSM) has been proposed to connect the smallness of neutrino masses with the spontaneous violation of parity [4,5,6]. In this work we propose instead that the ideal channel for probing the Dirac mass term of heavy neutrinos is through the purely leptonic decay WÆR → lÆN → lÆðN → l0ÆW∓ → lÆl0∓νÞ This channel has been previously studied in the context of the type I seesaw extension of the SM with fermion singlets in Ref. Assuming charge conjugation as the left-right symmetry for the minimal case, we explain the relationship between the Dirac mass matrix in terms of the heavy and light neutrino mass matrices. This connection is crucial to obtain the sensitivity to the Dirac mass.
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