Displaced heavy neutral lepton from new Higgs doublet

Abstract

Abstract Heavy neutral leptons N are introduced to explain the tiny neutrino masses via the seesaw mechanism. For proper small mixing parameter $$V_{\ell N},$$ V ℓ N , 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 $$\Phi _\nu $$ 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 $$W^\pm \rightarrow \ell ^\pm N$$ W ± → ℓ ± N decay, the branching ratios of new decays as $$H^\pm \rightarrow \ell ^\pm N$$ H ± → ℓ ± N are not suppressed when $$|V_{\ell N}|\gtrsim 10^{-16}.$$ | V ℓ N | ≳ 10 - 16 . 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 $$|V_{\ell N}|^2\gtrsim 10^{-18}$$ | V ℓ N | 2 ≳ 10 - 18 with $$m_N<m_{H^+},$$ m N < m H + , which covers the seesaw predicted value $$|V_{\ell N}|^2\sim m_\nu /m_N.$$ | V ℓ N | 2 ∼ m ν / m N . We could probe $$m_{H^+}\lesssim 1100$$ m H + ≲ 1100 GeV at the 14 TeV HL-LHC and $$m_{H^+}\lesssim 1490$$ m H + ≲ 1490 GeV at the 3 TeV CLIC.