LHC Signals for Singlet Neutrinos from a Natural Warped Seesaw (II)

Abstract

A natural seesaw mechanism for obtaining the observed size of SM neutrino masses can arise in a warped extra dimensional/composite Higgs framework. In a previous paper, we initiated the study of signals at the LHC for the associated $\sim$ TeV mass SM singlet neutrinos, within a canonical model of $SU(2{)}_L\times SU(2{)}_R\times U(1{)}_{B-L}$ (LR) symmetry in the composite sector, as motivated by consistency with the EW precision tests. Here, we investigate LHC signals in a different region of parameter space for the same model, where production of singlet neutrinos can occur from particles beyond those in usual LR models. Specifically, we assume that composite $(B-L)$ gauge boson is lighter than all the others in the EW sector. We show that the composite $(B-L)$ gauge boson can acquire a significant coupling to light quarks simply via mixing with elementary hypercharge gauge boson. Thus, the singlet neutrino can be pair-produced via decays of $(B-L)$ gauge boson, without a charged current counterpart. Furthermore, there is no decay for $(B-L)$ gauge boson directly into dibosons, unlike for the usual case of $W_R^{\pm }$ and $Z^{\prime }$. Independently of the above extension of the EW sector, we analyze production of singlet neutrinos in decays of composite partners of $SU(2{)}_L$ doublet leptons, which are absent in the usual LR models. In turn, these doublet leptons can be produced in composite $W_L$ decays. We show that $4-5\sigma$ signal can be achieved for both cases described above for the following spectrum with 3000 fb${}^{-1}$ luminosity: $2-2.5$ TeV composite gauge bosons, $1$ TeV composite doublet lepton (for the second case) and $500-750$ GeV singlet neutrino.

Comments: 45 pages, 17 figures