Displaced Heavy Neutral Lepton from New Higgs Doublet

Heavy neutral leptons N are introduced to explain the tiny neutrino masses via the seesaw mechanism. For proper small mixing parameter VN, the heavy neutral leptons N become long-lived, which leads to the displaced vertex signature at colliders. In this paper, we consider the displaced heavy neutral lepton from the neutrinophilic Higgs doublet Φ_ν decay. The new Higgs doublet with MeV scale VEV can naturally explain the tiny neutrino masses with TeV scale N. Different from current experimental searches via the W^±→ ^± N decay, the new decays as H^±→ ^± N are not suppressed by the small mixing parameter VN. Therefore, a larger parameter space is expected to be detected at colliders. We then investigate the promising region at the 14 TeV HL-LHC and the 3 TeV CLIC. According to our simulation, the DV signature could probe |VN|²10⁻¹⁹ with mN<mH⁺, which covers the seesaw predicted value |VN|²~ m_ν/mN. We could probe mH⁺1200 GeV at the 14 TeV HL-LHC and mH⁺1490 GeV at the 3 TeV CLIC.