Leptonic Scalars at the LHC

Abstract

We explore the collider prospects of neutrino non-standard interaction with a Standard Model (SM) gauge-singlet leptonic scalar $\varphi$ carrying two units of lepton-number-charge. These leptonic scalars are forbidden from interacting with the SM fermions at the renormalizable level and, if one allows for higher-dimensional operators, couple predominantly to SM neutrinos. For masses at or below the electroweak scale, $\varphi$ decays exclusively into neutrinos. Its characteristic production signature at hadron collider experiments like the LHC would be via the vector boson fusion process and leads to same-sign dileptons, two forward jets in opposite hemispheres, and missing transverse energy, i.e., $pp\to {\ell }_{\alpha }^{\pm }{\ell }_{\beta }^{\pm }jj+E_T^{\mathrm{miss}}$ ($\alpha ,\beta =e,\mu ,\tau$). Exploiting the final states of electrons and muons, we estimate, for the first time, the sensitivity of the LHC to these lepton-number-charged scalars. We show that the LHC sensitivity is largely complementary to that of low-energy precision measurements of the decays of charged leptons, charged mesons, $W$, $Z$ and the SM Higgs boson, as well as the neutrino beam experiments like MINOS, and searches for neutrino self-interactions at IceCube and in cosmological observations. For $\varphi$ mass larger than roughly 10 GeV, our projected LHC sensitivity would surpass all existing bounds.

Comments: 36 pages, 10 figures, 4 tables, some analysis and limits are updated or added, some UV-complete models are provided in the appendix, more references, version to appear in JHEP