Indirect probes of the trilinear Higgs coupling: gg → h and h → γγ

Abstract

In the framework of the Standard Model effective field theory, we examine the indirect constraints on the trilinear Higgs coupling λ that arise from Higgs production in gluon-gluon-fusion and diphoton Higgs decays. We calculate 2-loop contributions to the gg → h and h → γγ amplitudes that are affected by modifications of the trilinear Higgs-boson vertex. Based on our new results, we analyse the sensitivity of present and future measurements of the hgg and hγγ couplings to shifts in λ. Under the assumption that O 6 = −λ H † H 3 is the only dimension-6 operator that alters the trilinear Higgs interactions, we find that at present the considered loop-level probes provide stronger constraints than pp → 2h. At future high-energy colliders indirect O(5) determinations of the trilinear Higgs coupling may be possible, making precision measurements of gg → h and h → γγ a useful addition to direct extractions of λ through double-Higgs production.

Constraints on the trilinear Higgs coupling from vector boson fusion and associated Higgs production at the LHC

“…From this measurement the cross section times branching ratio for non-resonant SM Higgs-boson pair production is constrained to be less than 330 fb, which is approximately 29 times above the SM expectation of (σ 13 TeV From this formula we find that the ATLAS limit on the pp → 2h → 2b2b production cross section translates into the following 95% confidence level (CL) bound 5) if theoretical uncertainties are taken into account. Note that (7.5) improves on the bound ofc 6 ∈ [−15.5, 18.1] that has been derived in [30] from the ATLAS Run I searches for pp → hh [72][73][74] by around 35%. It follows that the combination λc 3 introduced in (2.3) can at present still deviate from the SM trilinear Higgs coupling λ by a factor of roughly 11.…”

“…Two example graphs are shown in the middle and on the right of figure 2. The results presented in [30,40] lead to…”

“…A second possibility consists in studying the effects that a modification of λ has at loop level in single-Higgs production. In fact, such indirect probes of the h 3 coupling have been first proposed in the context precision studies of e + e − → hZ [28,29] and subsequently extended to observables accessible at hadronic machines such as the LHC [30,31]. For both types of colliders it has been shown that future determination of λ via loop effects are complementary to the direct HL-LHC determination through pp → hh, since these probes can provide competitive constraints under the simplified assumption that newphysics effects dominantly modify the h 3 coupling.…”

“…This paper is a sequel to the article [30], in which two of us have calculated the O(λ) corrections to the gg → h and h → γγ processes that arise at the 2-loop level within the SM effective field theory (SMEFT). The discussion in the present paper focuses instead on associated (V h) and vector boson fusion (VBF) Higgs production.…”

The Z decay width in the SMEFT: y t and λ corrections at one loop

“…For results and discussion (with supporting calculations) characterizing various NLO corrections in the SMEFT see refs. [13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”