Abstract
In composite Higgs models the Higgs boson arises as a pseudo-Goldstone boson from a strongly-interacting sector. Fermion mass generation is possible through partial compositeness accompanied by the appearance of new heavy fermionic resonances. The Higgs couplings to the Standard Model (SM) particles and between the Higgs bosons themselves are modified with respect to the SM. Higgs pair production is sensitive to the trilinear Higgs self-coupling but also to anomalous couplings like the novel 2-Higgs-2-fermion coupling emerging in composite Higgs models. The QCD corrections to SM Higgs boson pair production are known to be large. In this paper we compute, in the limit of heavy loop particle masses, the next-to-leading order (NLO) QCD corrections to Higgs pair production in composite Higgs models without and with new heavy fermions. The relative QCD corrections are found to be almost insensitive both to the compositeness of the Higgs boson and to the details of the heavy fermion spectrum, since the leading order cross section dominantly factorizes. With the obtained results we investigate the question if, taking into account Higgs coupling constraints, new physics could first be seen in Higgs pair production. We find this to be the case in the high-luminosity option of the LHC for composite Higgs models with heavy fermions. We also investigate the invariant mass distributions at NLO QCD. While they are sensitive to the Higgs non-linearities and hence anomalous couplings, the influence of the heavy fermions is much less pronounced.
Highlights
We presented the next-to-leading order (NLO) QCD corrections to Higgs pair production via gluon fusion in the large quark mass approximation in composite Higgs models with and without new heavy fermionic resonances below the UV cut-off
We found that the K-factor of ∼ 1.7 is basically independent of the value of ξ and of the details of the fermion spectrum, as the leading order (LO) cross section dominantly factorizes
With the results of our NLO calculation, we addressed the question of whether new physics (NP) could emerge for the first time in Higgs pair production, taking into account the constraints on the Higgs couplings to Standard Model (SM) particles and from direct searches for new heavy fermions
Summary
In composite Higgs models the Higgs boson arises as a pseudo-Nambu Goldstone boson of a strongly interacting sector [104,105,106,107,108,109,110,111,112]. [90] by including higher terms in the expansion of the cross section in small external momenta Based on these findings, we will give the NLO QCD corrections for Higgs pair production in composite Higgs models in the LET approach. We call Higgs pair production to be sensitive to NP if the difference between the number of signal events S in the considered NP model and the corresponding number SSM in the SM exceeds a minimum of 3 statistical standard deviations, i.e. where BR denotes the branching ratio into the respective final states, L the integrated luminosity and A the acceptance due to cuts applied on the cross section. With the present bounds on ξ Higgs pair production in MCHM5 differs by more than 3σ from the SM prediction, the corresponding cross section is too small to be measurable, so that first signs of NP through this process are precluded
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