Abstract
We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders. We study the prospects for observing these processes at the LHC and a future 100 TeV pp collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements. Our study illustrates a strategy for systematically exploring the phenomenologically viable parameter space of this model, which we hope will be useful for future work.
Highlights
Gauge singlet scalar fields appear in many well-motivated extensions of the Standard Model (SM)
An attractive feature of such scenarios is that the singlet can give rise to a strong first-order electroweak phase transition (EWPT), as required for the mechanism of electroweak baryogenesis (EWB) [1,2,3], without large deviations in the predicted Standard Model-like Higgs properties
This is in contrast with scenarios like minimal supersymmetry, in which a strong first-order electroweak phase transition is excluded by a combination of Higgs measurements and direct searches for light scalar top quarks [4,5,6,7,8]
Summary
Gauge singlet scalar fields appear in many well-motivated extensions of the Standard Model (SM). Motivated by the observations above, in this study we address the possibility of directly probing the electroweak phase transition in singlet models via non-resonant scalar pair production involving the singlet-like state at hadron colliders. Searching for evidence of these processes at colliders can complement Higgs self-coupling and other precision measurements in their coverage of the parameter space, especially for small Higgs-singlet mixing angles We demonstrate this by comparing the various leading-order scalar pair production cross-sections across the parameter space of the model, and by studying the prospects for observing non-resonant ss production at the LHC and a future 100 TeV collider. Additional information regarding our renormalization scheme, the non-resonant scalar pair production cross-sections, the kinematic distributions relevant for our trilepton study, and our calculation of higher order effects on the effective ZZh coupling is included in appendices A, B, C, and D, respectively
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