Phenomenology of Charged Higgs Bosons in 2HDM at Future Lepton Colliders

In this presentation, I will synthesize comprehensive investigations into the phenomenology of charged Higgs bosons (H±H^\pmH±) within the framework of the Two-Higgs-Doublet Model (2HDM) at future high-energy lepton colliders. As a direct consequence of extending the Standard Model scalar sector, the discovery of H±H^\pmH± would provide unambiguous evidence for physics beyond the Standard Model and offer deep insights into the mechanism of electroweak symmetry breaking. We specifically focus on the comparative potential of muon (μ+μ−\mu^+\mu^-μ+μ−) and electron–positron (e+e−e^+e^-e+e−) machines, including proposed facilities such as the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). Our analysis covers a broad spectrum of production mechanisms, including:

* Pair and Single Production: μ+μ−→H+H−\mu^+\mu^- \to H^+H^-μ+μ−→H+H− and μ+μ−→W∓H±\mu^+\mu^- \to W^\mp H^\pmμ+μ−→W∓H±.
* Vector Boson Fusion (VBF): ℓ+ℓ−→ννˉH+H−\ell^+\ell^- \to \nu\bar{\nu}H^+H^-ℓ+ℓ−→ννˉH+H−, demonstrating that VBF becomes highly competitive with, and often surpasses, $2 \to 2$ processes at multi-TeV center-of-mass energies.
* Associated Production: ℓ+ℓ−→τ+ντH−\ell^+\ell^- \to \tau^+\nu_\tau H^-ℓ+ℓ−→τ+ντ​H−, ℓ+ℓ−→tbˉH−\ell^+\ell^- \to t\bar{b}H^-ℓ+ℓ−→tbˉH−, and production associated with neutral Higgs bosons (S=h,H,AS = h, H, AS=h,H,A) or ZZZ bosons.

A key finding of our research is the significant enhancement in production cross-sections at muon colliders. This is primarily attributed to the exchange of neutral Higgs bosons and unique sss-channel and ttt-channel diagrams, which leverage the significantly larger Yukawa couplings of the muon (mμ/me≈207m_\mu/m_e \approx 207mμ​/me​≈207) compared to the electron. Furthermore, we explore how specific symmetries, such as the discrete Z2Z_2Z2​ symmetry typically imposed to suppress flavor-changing neutral currents, influence the observed cross sections and branching ratios. We present updated results for various center-of-mass energies ranging from 500 GeV to 3 TeV, evaluating the sensitivity to different parameter spaces of the model. These findings highlight the critical role of muon colliders in exploring the scalar sector of the 2HDM with unprecedented precision and its implications for the underlying symmetries of nature.