Abstract
We discuss the current status of theoretical and experimental constraints on the real Higgs singlet extension of the Standard Model. For the second neutral (non-standard) Higgs boson we consider the full mass range from 1 GeV to 1 TeV accessible at past and current collider experiments. We separately discuss three scenarios, namely, the case where the second Higgs boson is lighter than, approximately equal to, or heavier than the discovered Higgs state at around 125 GeV. We investigate the impact of constraints from perturbative unitarity, electroweak precision data with a special focus on higher order contributions to the W boson mass, perturbativity of the couplings as well as vacuum stability. The latter two are tested up to a scale of 4 x 10^10 GeV using renormalization group equations. Direct collider constraints from Higgs signal rate measurements at the LHC and 95% C.L. exclusion limits from Higgs searches at LEP, Tevatron and LHC are included via the public codes HiggsSignals and HiggsBounds, respectively. We identify the strongest constraints in the different regions of parameter space. We comment on the collider phenomenology of the remaining viable parameter space and the prospects for a future discovery or exclusion at the LHC.
Highlights
Direct collider constraints from Higgs signal rate measurements at the LHC and 95 % confidence level exclusion limits from Higgs searches at LEP, Tevatron, and LHC are included via the public codes HiggsSignals and HiggsBounds, respectively
We separate the discussion of the parameter space into three different mass regions: (i) the high mass region, m H ∈ [130, 1000] GeV, where the lighter Higgs boson h is interpreted as the discovered Higgs state; (ii) the intermediate mass region, where both Higgs bosons h and H are located in the mass region [120, 130] GeV and potentially contribute to the measured signal rates, and (iii) the low mass region, mh ∈ [1, 120] GeV, where the heavier Higgs boson H is interpreted as the discovered Higgs state
We have investigated the theoretical and experimental limits on the parameter space of a real singlet extension of the SM Higgs sector, considering mass values of the second Higgs boson ranging from 1 GeV to 1 TeV, i.e. within the accessible mass range of past, current and future collider experiments
Summary
The real Higgs singlet extension of the SM is described in detail in Refs. [19,20,41,58]. The second condition, Eq (5), guarantees that the potential is bounded from below for large field values We assume that both Higgs fields and S have a non-zero VEV, denoted by v and x, respectively. The total width is given by tot = sin α × SM, tot + H→hh , where SM, tot denotes the total width of the SM Higgs boson with mass m H. It follows from Eq (10) that the light (heavy) Higgs boson couplings to SM particles are suppressed by cos α (sin α). The suppression of the production cross section of the two Higgs states induced by the mixing, which is given by sin α (cos α) for the heavy (light) Higgs, respectively;. The suppression of the Higgs decay modes to SM particles, which is realized if the competing decay mode H → hh is kinematically accessible
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