Triple Higgs couplings in the 2HDM: the complete picture

Abstract

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, $$\lambda _{hhh}/\lambda _{\mathrm{SM}}$$ λ hhh / λ SM , we find allowed intervals of $$\sim [{-0.5}, {1.3}]$$ ∼ [ - 0.5 , 1.3 ] in type I and $$\sim [{0.5}, {1.0}]$$ ∼ [ 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 $$\lambda _{hhH}$$ λ hhH between $$\sim -1.5$$ ∼ - 1.5 and $$\sim +1.5$$ ∼ + 1.5 in the four Yukawa types. For the triple Higgs couplings involving two heavy neutral Higgs bosons, $$\lambda _{hHH}$$ λ hHH and $$\lambda _{hAA}$$ λ hAA we find values between $$\sim -0.5$$ ∼ - 0.5 and $$\sim 16$$ ∼ 16 , and between $$\sim -1$$ ∼ - 1 and $$\sim 32$$ ∼ 32 for $$\lambda _{hH^+H^-}$$ λ h H + H - . These potentially large values could lead to strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy lepton colliders.

Fine-tuning in the 2HDM

“…Specific, partial, studies of the allowed parameter space in the 2HDM have been done for concrete models, see e.g. [59] for Type I; or addressing particular scenarios, like possibly sizeable triple Higgs couplings (such as h H H) [47,60,61], or in the context of possible experimental anomalies, such as the muon g − 2 [62].…”

Two Higgs doublets, effective interactions and a strong first-order electroweak phase transition

“…Higgs pair production is an important tool for fingerprinting an SFOEWPT, and the distance |1 − ξ d4 c | is directly correlated with expected Higgs pair production deviation. Current extrapolations of Higgs pair production to the 3/ab high-luminosity frontier indicate that the LHC should become sensitive enough to partially explore this region (see also the recent [117]), potentially assisted by discoveries in the t t channels. For more stronglycoupled Higgs interactions of the renormalisable 2HDM, the H → hh signature is more motivated as a signature for 2HDM discovery.…”