Probing Doubly Charged Higgs Bosons with Three-Body Associated Production at Future $e^+e^-$ Colliders

TL;DR

The paper investigates the discovery prospects for a doubly charged Higgs $H^{\pm\pm}$ in the 2HDM with a type-II seesaw sector (2HDMcT) at future $e^+e^-$ colliders. It emphasizes novel three-body production channels $e^+e^- \to H^{\pm\pm}H_1^{\mp}H_1^{\mp}$ and $e^+e^- \to H^{\pm\pm}H_1^{\mp}W^{\mp}$, conducting a thorough parameter-space scan under theory and experimental constraints and performing a detector-level MC analysis of the $4\ell+E_T^{\text{miss}}$ signature. The results show that these $2\to3$ processes can surpass conventional $2\to2$ production in large regions of parameter space, with cross sections up to ${\cal O}(10^2)$ fb for $\sqrt{s}=500$--$1500$ GeV, leading to promising discovery prospects at $\sqrt{s}=1$--$1.5$ TeV with a few ab$^{-1}$ of data. The study demonstrates the potential of lepton colliders to probe triplet Higgs scenarios beyond the conventional pair-production channels, especially when mass splittings and additional Higgs states enhance the $2\to3$ channels.

Abstract

We study the discovery prospects for a doubly charged Higgs boson $H^{\pm\pm}$ in the 2-Higgs Doublet Model with type-II seesaw (2HDMcT) at future $e^+e^-$ colliders. Focusing on the three-body channels $e^+e^- \to H^{\pm\pm}H_1^{\mp}H_1^{\mp}$ and $e^+e^- \to H^{\pm\pm}H_1^{\mp}W^{\mp}$, we scan the model parameter space subject to theoretical consistency as well as current collider, flavor and Electro-Weak Precision Observables (EWPOs). We find that these $2\to3$ production modes can exceed the conventional pair-production rate $e^+e^- \to H^{++}H^{--}$, followed by $H^{\pm\pm}\to H_1^{\pm}H_1^{\pm}$ and $H^{\pm}_1W^{\pm}$ decays, over wide regions, particularly above the $H^{\pm\pm}\to H_1^{\pm}H_1^{\pm}$ and $H^{\pm\pm}\to H_1^{\pm}W^{\pm}$ thresholds, reaching cross-sections up to ${\cal O}(10^2)$~fb for $\sqrt{s}=500$--$1500$~GeV. A detector-level analysis of the $4\ell + E_T^{\text{miss}}$ signature, including dominant multiboson and top quark backgrounds, shows that discovery sensitivity is achievable for $\sqrt{s}=1000$-$1500$~GeV with integrated luminosities in the few ab$^{-1}$ range, even in the presence of realistic systematic uncertainties.

Figures (9)

• Figure 1: Constraints on the diagonal entries of the neutrino mass matrix $M_\nu$ as functions of the lightest neutrino mass, $m_{\nu_1}$ for the NH (left) and $m_{\nu_3}$ for the IH (right). The phases are fixed to $\Phi_1 = 0$ and $\Phi_2 = 0$.
• Figure 2: Constraints on the off-diagonal elements entries of the neutrino mass matrix $M_\nu$ as functions of the lightest neutrino mass, $m_{\nu_1}$ for the NH (left) and $m_{\nu_3}$ for the IH (right). The phases are fixed to $\Phi_1 = 0$ and $\Phi_2 = 0$.
• Figure 3: Tree-level generic Feynman diagrams for $e^-e^+\to H^{++}H_1^-H_1^-$ are shown in $(d_{1,...,7})$. For all diagrams $S_j^\pm$ refers to $H_1^{\pm}$ or $H_2^{\pm}$.
• Figure 4: Tree-level generic Feynman diagrams for $e^-e^+\to H^{++}H_1^-W^-$ are shown in $(d_{1,...,8})$. For all diagrams $S_j^\pm$ refers to $H_1^{\pm}$ or $H_2^{\pm}$. Furthermore, $V=\gamma,Z$.
• Figure 5: Mass splitting between $H^{\pm\pm}$ and $H_1^{\pm}$ (left), and between $H^{\pm\pm}$ and $H_2^{\pm}$ (right).