Triple Higgs couplings in the 2HDM: the complete picture

The measurement of the triple Higgs coupling is one of the main tasks of the (HL-)LHC and future lepton colliders. Similarly, triple Higgs couplings involving BSM Higgs bosons are of high interest. Within the framework of Two Higgs Doublet Models (2HDM) we investigate the allowed ranges for all triple Higgs couplings involving at least one light, SM-like Higgs boson. We present newly the allowed ranges for 2HDM type III and IV and update the results within the type I and II. We take into account theoretical constraints from unitarity and stability, experimental constraints from direct BSM Higgs-boson searches, measurements of the rates of the SM-like Higgs-boson at the LHC, as well as flavor observables and electroweak precision data. For the SM-type triple Higgs coupling w.r.t. its SM value, lambda(hhh)/lambda(SM), we find allowed intervals of similar to [-0.5, 1.3] in type I and similar to [0.5, 1.0] in the other Yukawa types. These allowed ranges have important implications for the experimental determination of this coupling at future collider experiments. We find the coupling lambda(hhH) between similar to -1.5 and similar to +1.5 in the four Yukawa types. For the triple Higgs couplings involving two heavy neutral Higgs bosons, lambda(hHH) and lambda(hAA) we find values between similar to -0.5 and similar to 16, and between similar to -1 and similar to 32 for lambda(hH+ H-). These potentially large values could lead to strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy lepton colliders.

Automated summary

This study investigates the allowed ranges for triple Higgs couplings involving at least one light, SM-like Higgs boson within the framework of Two Higgs Doublet Models (2HDM). The results have important implications for the experimental determination of this coupling at future collider experiments, and potentially large values could lead to strongly enhanced production of two Higgs-bosons at high-energy colliders.