An Exploratory study of Higgs-boson pair production

TL;DR

This work develops an exploratory, model-independent framework to probe the Higgs trilinear coupling via Higgs-boson pair production in gluon fusion, explicitly allowing CP violation in the top-Yukawa sector and a dim-5 $ttHH$ contact interaction. By decomposing the cross section into triangle, box, and contact contributions with energy- and cut-dependent coefficients, it provides a practical method to infer $\lambda_{3H}$ from multi-parameter fits. The study leverages the $HH \to \gamma\gamma b\bar b$ decay mode and $\Delta R$ observables to separate diagrammatic contributions, presenting detector-level sensitivity estimates at 14 TeV LHC and a future 100 TeV collider under several CP scenarios. The results indicate that, with cross-section measurements at ~25% precision and coordinated multi-channel analyses, one can constrain or detect a nonzero Higgs self-coupling and map the allowed CP-violating and contact-interaction parameter space, highlighting the importance of combining LHC results with future collider information.Overall, the paper demonstrates the viability of using angular and kinematic discriminants in Higgs-pair production to access the Higgs self-coupling and potential new physics in the Higgs sector.

Abstract

Higgs-boson pair production is well known being capable to probe the trilinear self-coupling of the Higgs boson, which is one of the important ingredients of the Higgs sector itself. Pair production then depends on the top-quark Yukawa coupling $g_t^{S,P}$, Higgs trilinear coupling $λ_{3H}$, and a possible dim-5 contact-type $ttHH$ coupling $g_{tt}^{S,P}$, which may appear in some higher representations of the Higgs sector. We take into account the possibility that the top-Yukawa and the $ttHH$ couplings involved can be CP violating. We calculate the cross sections and the interference terms as coefficients of the square or the 4th power of each coupling $(g_t^{S,P}, λ_{3H}, g_{tt}^{S,P})$ at various stages of cuts, such that the desired cross section under various cuts can be obtained by simply inputing the couplings. We employ the $H H \to γγb \bar b$ decay mode of the Higgs-boson pair to investigate the possibility of disentangle the triangle diagram from the box digram so as to have a clean probe of the trilinear coupling at the LHC. We found that the angular separation between the $b$ and $\bar b$ and that between the two photons is useful. We obtain the sensitivity reach of each pair of couplings at the 14 TeV LHC and the future 100 TeV pp machine. Finally, we also comment on using the $b\bar b τ^+ τ^-$ decay mode in Appendix.