[Paper Review] Supersymmetry after the Higgs discovery and its LHC phenomenology

Sho Iwamoto|arXiv (Cornell University)|May 3, 2013

Particle physics theoretical and experimental studies129 references3 citations

TL;DR

This dissertation proposes the V-GMSB model, an extension of gauge-mediated supersymmetry (GMSB) with vector-like matters (V-MSSM), to reconcile the 126 GeV Higgs boson mass with the muon anomalous magnetic moment anomaly. By introducing a (10+10) SU(5) decuplet of vector-like quarks and leptons, the model raises the Higgs mass through loop corrections, allowing lighter stop quarks (O(1–2 TeV)) and reviving viable CMSSM and GMSB scenarios. The key result is that the 126 GeV Higgs and 2σ-level explanation of the muon g−2 anomaly can be simultaneously realized, with vector-like quarks constrained to MV ≲1.2 TeV.

ABSTRACT

Under the minimal SUSY standard model (MSSM), the discrepancy in the muon g-2 suggests the SUSY particles are of order 100 GeV, which is also supported by discussions on the little hierarchy problem. However, the LHC experiments have found no scalar-quarks or gluinos in such mass range, and moreover, the Higgs boson mass of 126 GeV requires, within the MSSM framework, the scalar-top mass of order 1-10 TeV. This current status forces us to abandon the simplest supersymmetry-breaking frameworks of the CMSSM and the GMSB scenarios. The V-MSSM is investigated in this dissertation, which is proposed as an extension of the MSSM with a (10 + 10bar) pair of the SU(5) decuplets. In the framework the Higgs mass is increased by effect from the extra matters, and thus the 126 GeV is achieved with the scalar-top having a lighter mass. This fact resurrects the CMSSM and the GMSB scenarios. This dissertation examines the GMSB scenario under the V-MSSM; it is called V-GMSB scenario. It is shown that the V-GMSB has a potential to realize the 126 GeV mass of the Higgs boson with holding the explanation of the muon magnetic moment discrepancy, if the masses of the extra quarks are approximately less than 1.2 TeV. Constraints on the V-GMSB from the LHC experiments are discussed then; it is concluded that the gluino mass must be approximately heavier than 1.1 TeV, and that the extra quarks be heavier than 300-650 GeV depending on the decay branches of them. LHC prospects are briefly discussed. As the extra quarks are expected to be approximately less than 1.2 TeV, searches for the particles are of great interest at the 14 TeV LHC; constraints from the supersymmetry search, especially on the gluino mass, are expected to be much improved there. Therefore, it is expected that the fate of the V-GMSB is adjudicated at the court of the 14 TeV LHC.

Motivation & Objective

• To resolve the tension between the 126 GeV Higgs boson mass and the muon anomalous magnetic moment (g−2) anomaly within supersymmetric models.
• To revive the CMSSM and GMSB scenarios, which were previously ruled out due to the high Higgs mass and lack of SUSY signals.
• To construct a viable GMSB framework with vector-like matters that explains both the Higgs mass and the muon g−2 anomaly without fine-tuning.
• To constrain the mass scale of vector-like quarks and leptons using LHC SUSY searches and vacuum stability bounds.
• To provide a phenomenologically viable path forward for supersymmetry after the Higgs discovery, consistent with SU(5) grand unification.

Proposed method

• Proposes the V-MSSM extension of the MSSM by introducing a (10+10) pair of SU(5) vector-like matter multiplets.
• Calculates radiative corrections to the Higgs mass from the vector-like quarks and leptons, enhancing the tree-level Higgs mass to 126 GeV.
• Applies gauge-mediated supersymmetry breaking (GMSB) with the vector-like sector, preserving the freedom from flavor and CP problems.
• Performs vacuum stability analysis to constrain the parameter space, particularly the vector-like mass scale MV.
• Uses Monte Carlo simulations and LHC search constraints (e.g., ATLAS b-tagging, chargino/neutralino pair production) to test phenomenological viability.
• Combines constraints from muon g−2, Higgs mass, and LHC searches to identify viable regions in the parameter space.

Experimental results

Research questions

• RQ1 Can the 126 GeV Higgs boson mass be achieved in a GMSB model without requiring extremely heavy stops?
• RQ2 Can the muon g−2 anomaly be explained within a GMSB framework that also satisfies the 126 GeV Higgs mass constraint?
• RQ3 What are the phenomenological signatures of vector-like quarks and leptons in the V-GMSB model at the LHC?
• RQ4 How does the inclusion of vector-like matters affect vacuum stability in extended GMSB models?
• RQ5 What are the upper bounds on the vector-like quark mass scale MV consistent with current LHC data and theoretical constraints?

Key findings

• The V-GMSB model successfully realizes the 126 GeV Higgs boson mass with stop masses in the 1–2 TeV range, resolving the tension with the CMSSM and GMSB scenarios.
• The muon g−2 anomaly can be explained at the 2σ level within the V-GMSB framework, while the 1σ-level explanation is excluded by LHC SUSY searches.
• The vector-like quark and lepton mass scale MV is constrained to be less than 1.2 TeV, implying the lightest vector-like quark t′1 is lighter than ≲1.1 TeV.
• The model predicts that the 14 TeV LHC run with O(100) fb−1 luminosity will have sufficient sensitivity to discover vector-like quarks if they are within the 1.1 TeV mass range.
• The V-GMSB model provides a viable path to reconcile the Higgs mass, muon g−2, and LHC constraints, while preserving the theoretical advantages of GMSB.
• Vacuum stability bounds further constrain the parameter space, favoring moderate values of MV and ensuring long-term stability of the electroweak vacuum.