Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at s=13 TeV

New constraints on extended scalar sectors from the trilinear Higgs coupling

“…All these constraints are applied using ScannerS [14] -except (ii) and (iii), which we evaluate separately. For parameter points passing all constraints, we compute 𝜅 𝜆 at one and two loops -which we denote 𝜅 (1) 𝜆 and 𝜅 (2) 𝜆 . For the parameter scan, we impose 𝑀 ℎ = 125 GeV and 𝛼 = 𝛽 − 𝜋/2, while the BSM scalar masses are varied in the range [300 GeV, 1500 GeV], tan 𝛽 in [0.8, 50], and 𝑚 2 12 in [0, 4 • 10 6 GeV 2 ].…”

“…This ensures that the tree-level couplings of ℎ are exactly equal to their SM values, and in particular that (𝜆 ℎℎℎ ) (0) = (𝜆 SM ℎℎℎ ) (0) = 3𝑚 2 ℎ /𝑣. The remaining input parameters for the numerical analysis are 𝑚 𝐻 , 𝑚 𝐴 , 𝑚 𝐻 ± , 𝑀 2 = 𝑚 2 12 /(sin 𝛽 cos 𝛽), and tan 𝛽 ≡ 𝑣 2 /𝑣 1 . For our one-(1L) and two-loop (2L) predictions, we employ results for 𝜆 ℎℎℎ from Refs.…”

“…[4] including the dominant 2L corrections (arising from heavy BSM scalars as well as the top quark) in a number of BSM models, including an aligned version of the 2HDM. The largest type of quartic coupling entering corrections to 𝜆 ℎℎℎ , both at one and two loops, are those between two SM-like and two heavy BSM Higgs bosons, of the form 2 , where Φ = 𝐻, 𝐴, 𝐻 ± and where one external Higgs boson ℎ is potentially replaced by a vacuum expectation value.…”

“…The experimental limits on 𝜅 𝜆 from Higgs-boson pair production [2] do not only rely on the assumption that all other Higgs couplings are SM-like (which is true in the alignment limit) but also that non-resonant Higgs-boson pair production only deviates from the SM via a modified value of 𝜆 ℎℎℎ . However, in the 2HDM, the additional Higgs bosons can in principle cause further modifications of Higgs-boson pair production.…”

“…At present, the best bounds on 𝜆 ℎℎℎ , expressed in terms of the coupling modifier 𝜅 𝜆 ≡ 𝜆 ℎℎℎ /(𝜆 SM ℎℎℎ ) (0) , are −0.4 < 𝜅 𝜆 < 6.3 at 95% C.L. [2], while more precise determinations are expected at future colliders [3].…”