Neutral scalar pair productions through $W$-boson fusion at multi--TeV muon colliders

TL;DR

This work provides the first full one-loop electroweak corrections to the SM di-Higgs process μ− μ+ → W± W∓ → hh and then analyzes neutral scalar pair production via W-boson fusion at multi-TeV muon colliders within the THDM. By scanning the THDM Type-X and Type-Y parameter spaces under strict theoretical and experimental constraints, it introduces the enhancement factor μ_hh (THDM vs SM) and finds μ_hh can reach about 3 in Type-X but lies between 0.91 and 0.96 in Type-Y. It also studies CP-odd Higgs pair production via WW fusion, showing in Type-Y at √s = 10 TeV with L = 10^4 fb−1 that the final state tt bb with leptonic top decays can achieve >2σ significance at several viable points, though most points stay below 5σ. Overall, the results demonstrate the potential of future muon colliders to probe extended scalar sectors and electroweak symmetry-breaking dynamics, with clear discriminants between THDM types and accessible CP-odd states.

Abstract

Full one-loop electroweak radiative corrections to $μ^- μ^+ \to W^\pm W^\mp \to hh$ in the Standard Model are computed for the first time in this work. We then evaluate neutral scalar pair production through vector boson fusion at multi--TeV muon colliders within Two-Higgs-Doublet Model (THDM). In the phenomenological analysis, the enhancement factor, defined as the ratio of the cross sections for SM-like Higgs pair production in the THDM with respect to the corresponding ones in the SM, is examined over the viable regions of the parameter space in the Type-X and Type-Y THDMs. Our findings show that this ratio can reach a factor of $3$ in several regions within the valid parameter space of the Type-X THDM, whereas it ranges from $0.91$ to $0.96$ over the entire parameter space of the Type-Y THDM. Finally, we scan the cross sections for double CP-odd Higgs production over the updated parameter space of the Type-X and Type-Y THDMs. In the Type-Y case at $\sqrt{s} = 10$~TeV with an integrated luminosity of $\mathcal{L} = 10000~\text{fb}^{-1}$, CP-odd Higgs pair production in the $t\bar{t}b\bar{b}$ final state, with subsequent top-quark decays into leptons and bottom quarks taken into account, can be tested with a statistical significance exceeding the $2σ$ level at several viable parameter points.

Figures (7)

• Figure 1: The parameter space for six independent parameters of THDM type-X on the left and type-Y on the right. The upper-plots show for scatter plots of $m_A-m_H, m_{H^\pm}-m_H$ and $m_{H^\pm}-m_A$. While lower-plots are for scatter plots of $m_{12}^2, m_A$ and the mixing angle $t_B$.
• Figure 2: The cross sections for the process $\mu^- \mu^+ \to W^\pm W^\mp \to hh$ and full electroweak radiative corrections are shown as a function of the center-of-mass (CoM) energy.
• Figure 3: The differential cross sections with respect to $p_T^{h}$ and the rapidity $\eta^h$ are shown. The red line corresponds to the tree-level cross-sections, while the blue line represents the fully corrected cross sections.
• Figure 4: The enhancement factor $\mu_{hh}$ is scanned over the $\tan\beta$ and $m_{H}$ parameter space, with the Type-X THDM shown in the left panels and the Type-Y THDM shown in the right panels. The results are presented at a center-of-mass energy of $3$ TeV in the two upper plots and at $10$ TeV in the two lower plots.
• Figure 5: The branching ratios for the decays $A \to t\bar{t}$ (left panel) and $A \to b\bar{b}$ (right panel) are shown in the parameter space of $m_A$ and $\tan\beta$. The results for the Type-X THDM are presented in the upper panels, while the corresponding decay rates for the Type-Y THDM are shown in the lower panels.