LHC signals for singlet neutrinos from a natural warped seesaw mechanism. I

Abstract

Recently, it was shown in K. Agashe et al. [Phys. Rev. D 94, 013001 (2016)] that a straightforward implementation of the type I seesaw mechanism in a warped extra dimensional framework is in reality a natural realization of "inverse" seesaw; i.e., the Standard Model (SM) neutrino mass is dominantly generated by exchange of pseudo-Dirac TeV-mass SM singlet neutrinos. By the AdS/CFT correspondence, this scenario is dual to these singlet particles being composites of some new strong dynamics, along with the SM Higgs boson (and possibly the top quark), with the rest of the SM particles being mostly elementary. We study signals from production of these heavy neutrinos at the Large Hadron Collider (LHC). We focus on the scenario where the strong sector has a global SU(2)(L) x SU(2)(R) x U(1)(X) symmetry; such a left-right (LR) structure being motivated by consistency with the electroweak (EW) precision tests. The singlet neutrinos are charged under SU(2)(R) x U(1)(X) symmetry, thus can be produced from W-R(+/-) exchange, as in four-dimensional LR symmetric models. However, the direct coupling of light quarks to W-R(+/-) is negligible, due to W-R(+/-) also being composite (cf. four-dimensional LR models); nonetheless, a sizable coupling can be induced by mixings among the various types of W-perpendicular to bosons. Furthermore, W-R(+/-) decays dominantly into the singlet and composite partner of charged lepton (cf. SM lepton itself in four-dimensional LR model). This heavy charged lepton, in turn, decays into SM lepton, plus Z/Higgs, thus the latter can be used for extra identification of the signal. For a benchmark scenario with W-R(+/-) of mass 2 TeV and singlet neutrino of mass 750 GeV, we find that, in both the dilepton thorn dijet + Higgs and trilepton + Higgs channels, significant evidence can be seen at the 14 TeV LHC for an integrated luminosity of 300 fb(-1) and that even discovery is possible with slightly more luminosity.