minimal supersymmetric standard model

minimal supersymmetric standard model
Lucas Taylor / CERN · CC BY-SA 3.0 · source
Name	Minimal Supersymmetric Standard Model
Type	Quantum field theory

minimal supersymmetric standard model. The minimal supersymmetric standard model is a theoretical extension of the Standard Model that incorporates supersymmetry to relate bosons and fermions, aiming to address the hierarchy problem and provide candidates for dark matter. It was developed in the late 1970s and 1980s alongside work by researchers associated with institutions such as CERN, Fermilab, and SLAC National Accelerator Laboratory, and has been central to experimental programs at the Large Hadron Collider and theoretical programs at universities like Harvard University, Princeton University, and University of Cambridge. The model's minimal field content and constrained parameter set make it a benchmark for searches at experiments including ATLAS (experiment), CMS (experiment), and LEP.

Overview and Motivation

The MSSM extends the Standard Model gauge group and particle spectrum by introducing superpartners for quarks, leptons, gauge bosons, and the Higgs boson, motivated by attempts to stabilize the electroweak scale against radiative corrections as emphasized in work related to the hierarchy problem and the naturalness principle. Early proponents connected supersymmetry to grand unification studied in contexts like SU(5), SO(10), and E6 (mathematics), noting that supersymmetric renormalization group running improves gauge coupling unification as explored by groups at CERN and SLAC National Accelerator Laboratory. The MSSM also supplies weakly interacting massive particle candidates for dark matter such as the lightest neutralino, which entered discussions at conferences including ICHEP and initiatives like the Dark Matter Research Centre.

Field Content and Superpotential

In the MSSM the chiral supermultiplets correspond to the three generations of quark and lepton superfields linked to phenomenology explored by scholars at Caltech and Massachusetts Institute of Technology, and two Higgs doublet superfields H_u and H_d required for anomaly cancellation and holomorphicity as emphasized in lectures at Princeton University and University of Oxford. Gauge supermultiplets for SU(3) color, SU(2) weak isospin, and U(1) hypercharge mirror the Standard Model structure analyzed at CERN and in textbooks used at Yale University and Stanford University. The renormalizable superpotential contains Yukawa interactions generating masses via electroweak symmetry breaking studied at DESY and a μ term whose origin motivated mechanisms like the Giudice–Masiero mechanism and proposals from researchers at University of Michigan and University of California, Berkeley.

Soft Supersymmetry Breaking and Parameters

Supersymmetry must be broken to match observed particle spectra, implemented via soft terms—gaugino masses, scalar masses, and trilinear A-terms—parameters explored in phenomenological scans by groups at Fermilab and CERN. Mediation schemes such as gravity mediation linked to supergravity frameworks at University of California, Santa Barbara, gauge mediation developed in collaborations involving University of Cambridge, and anomaly mediation studied at Harvard University produce distinct boundary conditions for the MSSM parameter set, which is often constrained in simplified scenarios like the CMSSM and mSUGRA referenced in experimental analyses by ATLAS (experiment) and CMS (experiment). Global fits performed by collaborations including MasterCode and theoretical groups at University of Edinburgh map soft parameter spaces against data from Tevatron and Large Hadron Collider searches.

Mass Spectrum and Mixing

The MSSM predicts extended mass matrices involving neutralinos, charginos, squarks, and sleptons, with mixing structures analogous to quark flavor mixing described in the context of the Cabibbo–Kobayashi–Maskawa matrix and lepton flavor studies informed by results from Super-Kamiokande and SNO. Radiative corrections to the Higgs sector, especially the light CP-even Higgs mass, were calculated in seminal papers from authors affiliated with University of Cambridge and University of Zurich and constrained by the Higgs discovery at CERN's Large Hadron Collider experiments ATLAS (experiment) and CMS (experiment), which measured a ~125 GeV scalar consistent with MSSM expectations only for substantial stop-sector contributions computed in tools from groups at KIT and IFT (Instituto de Física Teórica). Flavor-changing and CP-violating effects are constrained by measurements at Belle (experiment), BaBar, and LHCb.

Phenomenology and Experimental Constraints

Collider signatures of the MSSM—missing transverse energy, multijet plus lepton final states, and long-lived particle tracks—have driven search strategies at ATLAS (experiment), CMS (experiment), and earlier at LEP and Tevatron. Direct detection experiments like XENON and LUX and indirect searches using observations from Fermi Gamma-ray Space Telescope and AMS-02 set limits on neutralino dark matter properties that complement collider bounds from runs at Large Hadron Collider. Precision observables such as the anomalous magnetic moment measured at Brookhaven National Laboratory and later experiments at Fermilab and electroweak fits performed by collaborations at CERN impose further constraints on MSSM parameter regions studied by theoretical groups at Imperial College London and University of Chicago.

Theoretical Issues and Extensions

Despite its virtues, the MSSM faces challenges including the μ problem, the little hierarchy problem, and tension with null results from direct searches, motivating extensions like the Next-to-Minimal Supersymmetric Standard Model developed in collaborations at University of Bonn and Max Planck Institute for Physics, gauge-extended models tied to U(1)' symmetries explored at University of Tokyo, and models incorporating R-parity violation discussed in workshops at KITP. Embedding the MSSM in frameworks such as string theory constructions investigated at Institute for Advanced Study and Perimeter Institute continues to link particle phenomenology with cosmology programs at Planck (spacecraft) and WMAP, while ongoing experimental programs at Large Hadron Collider and proposed facilities like the International Linear Collider and Future Circular Collider will further probe MSSM-inspired physics.

Category:Supersymmetric quantum field theories