Abstract
We study the double Higgs boson production processes $e^+e^- \to hh f\bar{f}$ ($f\neq t$) with $h$ being the 125 GeV Higgs boson in the two-Higgs-doublet model with a softly-broken $Z_2$ symmetry. The cross section can be significantly enhanced, typically a few hundreds percent, as compared to the standard model prediction due to resonant effects of heavy neutral Higgs bosons, which becomes important in the case without the alignment limit. We find a strong correlation between the enhancement factor of the cross section and the scaling factor of the $hf\bar{f}$ couplings under constraints from perturbative unitarity, vacuum stability and current experimental data at the LHC as well as the electroweak precision data.
Highlights
Various signatures of the discovered Higgs boson at the LHC [1,2] show that its properties such as observed production cross sections and decay branching ratios are consistent with those predicted in the standard model (SM) [3]
If deviations in the Higgs boson couplings are detected in future, we expect the sizable enhancement of the double Higgs boson production as well
We have discussed the correlation between the scaling factor of the Yukawa coupling for the SM like Higgs boson κf and the ratio of the cross section for the eþe− → hhff (f ≠ t) process normalized to the SM prediction in the type-I two-Higgs-doublet model (THDM)
Summary
Various signatures of the discovered Higgs boson at the LHC [1,2] show that its properties such as observed production cross sections and decay branching ratios are consistent with those predicted in the standard model (SM) [3]. We focus on the cross section of double Higgs boson production processes at future eþe− colliders as another important observable regarding the indirect search of the THDM. It would be worth mentioning that taking sβ−α → 1, all the hVV (V 1⁄4 W, Z), hffand hhh couplings become the same values as in the SM at tree level This limit has been known as the alignment limit, where the SM-like Higgs boson h completely comes from the doublet Φ in the Higgs bases in Eq (2)
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