Resonant Multi-Scalar Production in the Generic Complex Singlet Model in the Multi-TeV Region

Abstract

We develop benchmarks for resonant di-scalar production in the generic complex singlet scalar extension of the Standard Model (SM), which contains two new scalars. These benchmarks maximize di-scalar resonant production: $pp\to h_2\to h_1{h}_1/h_1{h}_3/h_3{h}_3$, where $h_1$ is the observed SM-like Higgs boson and $h_{2,3}$ are new scalars. The decays $h_2\to h_1{h}_3$ and $h_2\to h_3{h}_3$ may be the only way to discover $h_3$, leading to a discovery of two new scalars at once. Current LHC and projected future collider (HL-LHC, FCC-ee, ILC500) constraints are used to produce benchmarks at the HL-LHC for $h_2$ masses between 250 GeV and 1 TeV and a future $pp$ collider for $h_2$ masses between 250 GeV and 12 TeV. We update the current LHC bounds on the singlet-Higgs boson mixing angle. As the mass of $h_2$ increases, certain limiting behaviors of the maximum rates are uncovered due to theoretical constraints on the parameters. These limits, which can be derived analytically, are $\mathrm{BR}(h_2\to h_1{h}_1)\to 0.25$, $\mathrm{BR}(h_2\to h_3{h}_3)\to 0.5$, and $\mathrm{BR}(h_2\to h_1{h}_3)\to 0$. It can also be shown that the maximum rates of $pp\to h_2\to h_1{h}_1/h_3{h}_3$ approach the same value. Hence, all three $h_2\to h_i{h}_j$ decays are promising discovery modes for $h_2$ masses below $\mathcal{O}(1\mathrm{TeV})$, while above $\mathcal{O}(1\mathrm{TeV})$ the decays $h_2\to h_1{h}_1/h_3{h}_3$ are more encouraging. Masses for $h_3$ are chosen to produce a large range of signatures including multi-b, multi-vector boson, and multi-$h_1$ production. The behavior of the maximum rates imply that in the multi-TeV region this model may be discovered in the Higgs quartet production mode before Higgs triple production is observed. The maximum di- and four Higgs production rates are similar in the multi-TeV range.

v2: matches version accepted by PRD, typos fixed, references added, discussion expanded, results unchanged, 28 pgs+21 pgs of appendices and references, 9 figures; v1: 27 pages+20 pages of appendices and references, 9 figures