Status of the Higgs Singlet Extension of the Standard Model after LHC Run 1 (1501.02234v2)

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.

• The paper rigorously examines the viability of a real singlet scalar extension to the Standard Model, exploring mixing effects with the 125 GeV Higgs boson across a mass range of 1 GeV to 1 TeV.
• It employs advanced tools like HiggsBounds and HiggsSignals to assess experimental and theoretical constraints, including electroweak precision data and vacuum stability up to 4 x 10^10 GeV.
• The study outlines future collider prospects and challenges, emphasizing the need for improved sensitivity to detect non-standard Higgs bosons and uncover potential new physics.

Insightful Overview of the Higgs Singlet Extension of the Standard Model Post-LHC Run 1

In the given paper, Robens and Stefaniak meticulously analyze the viability of the Higgs singlet extension of the Standard Model (SM), accounting for various theoretical and experimental constraints borne out of the LHC's initial phase. This exploration is particularly pertinent in light of the inconclusive evidence for additional scalar bosons, which, if discovered, could provide insight into potential Beyond Standard Model (BSM) physics.

Expansion of the Higgs Sector

The paper in question revolves around the simplest extension to the SM Higgs sector: the inclusion of a real singlet scalar field. This modest expansion affects the scalar potential and induces mixing between the SM-like Higgs boson and a new singlet scalar. The resulting model posits a second Higgs boson with mass capability extending from as low as 1 GeV to 1 TeV—a range dictated by the operational scope of previous and existing collider experiments. The model's fertile ground of potential discoveries lies in the distinct scenarios where the non-standard Higgs boson is lighter than, comparable to, or heavier than the known 125 GeV Higgs.

Constraints on the New Higgs Boson

Robens and Stefaniak rigorously interrogate experimental constraints, including collider results from LEP, Tevatron, and the LHC, using tools like HiggsBounds and HiggsSignals. Their focus spans perturbative unitarity, electroweak precision data, and vacuum stability, the latter examined up to an energy scale of 4 x 10^10 GeV via renormalization group equations. Notably, results from the LHC's Run 1 notably illustrate the challenge of fitting this singlet model into existing observations, particularly under the scrutiny of signal strength measurements.

Parameter Space and Constraints

The analysis delineates three critical regions of the parameter space: light, heavy, and intermediate masses. In the heavy mass scenario (m > 125 GeV), the non-standard Higgs boson must reconcile with stringent cross-section limits derived from a lack of new signal excesses. Conversely, in the low mass region, stringent LEP constraints heavily steered by Precision Electroweak Measurement results come to the fore.

Collider Phenomenology and Future Prospects

The paper proceeds to glimpse into future collider possibilities, emphasizing the LHC's extended runs and also floated the prospect of high precision with future experimental facilities, such as the proposed ILC. These scenarios hold promise for detecting the Higgs-to-Higgs decay channels or subtle deviations in SM predicted channels, offering telltale signs of new physics. Despite presenting ripe opportunities, these require sensitivity enhancements and more data.

Interactions and the Challenge of Integration

Importantly, the paper reflects on the theoretical underpinnings of the singlet extension, underscoring perturbativity constraints and vacuum stability. Rigorous renormalization group analysis elucidates nuanced interaction scales, which are critical for ensuring theoretical consistency across high-energy interactions.

Conclusion

Robens and Stefaniak’s paper presents a sophisticated inquiry into the singlet extended Higgs model, thoroughly analyzing constraints post-LHC Run 1. The outcomes furnish a consequential exploration into the parametric viability under contemporary collider constraints and outline future challenges and opportunities for uncovering new physics. As we advance into the next phases of experimental tests, this paper lays a foundation not only for potential discoveries but also for the intricate theoretical modeling of extended scalar sectors in particle physics.