Resonant multiscalar production in the generic complex singlet model in the multi-TeV region

We develop benchmarks for resonant discalar production in the generic complex singlet scalar extension of the Standard Model (SM) with no additional symmetries, which contains two new scalars. These benchmarks maximize discalar resonant production modes at future pp colliders: pp→h2→h1h1, pp→h2→h1h3, and pp→h2→h3h3, where h1 is the observed SM-like Higgs boson and h2,3 are new scalars. The decays h2→h1h3 and h2→h3h3 may be the only way to discover h3, leading to a discovery of two new scalars at once. Current LHC and projected future collider (HL-LHC, FCC-ee+HL-LHC, ILC500+HL-LHC) constraints on this model are used to produce benchmarks at the HL-LHC for h2 masses between 250 GeV and 1 TeV and a future pp collider (FCC-hh) for h2 masses between 250 GeV and 12 TeV. We update the current LHC bounds on the singlet-Higgs boson mixing angle for these benchmarks. As the mass of h2 approaches the multi-TeV region, certain limiting behaviors of the maximum rates are uncovered due to theoretical constraints on the parameters. These limits, which can be derived analytically, are BR(h2→h1h1)→0.25, BR(h2→h3h3)→0.5, and BR(h2→h1h3)→0. It can also be shown that the maximum rates of pp→h2→h1h1 and pp→h2→h3h3 approach the same value. Hence, all three h2→hihj decays are promising discovery modes for h2 masses at and below O(1 TeV), while above O(1 TeV) the decays h2→h1h1 and h2→h3h3 are more encouraging. We choose benchmark masses for h3 to produce a large range of decay signatures including multi-b, multivector boson, and multi-SM-like Higgs production. As we will show, the behavior of the maximum rates leads to the surprising conclusion that in the multi-TeV region this model may be discovered in the Higgs quartet production mode via h2→h3h3→4h1 decays before Higgs triple production is observed. The maximum di- and four Higgs production rates are similar in the multi-TeV range. Published by the American Physical Society 2024