Split SUSY

Split SUSY
Lucas Taylor / CERN · CC BY-SA 3.0 · source
Name	Split supersymmetry
Field	Particle physics
Introduced	2004
Key people	Nima Arkani-Hamed, Savas Dimopoulos, Gian Francesco Giudice, Matthew Strassler
Concepts	Supersymmetry, Higgs boson, dark matter

Split SUSY

Split SUSY is a class of supersymmetric models proposing a large mass split between scalar superpartners and fermionic gauginos and higgsinos. It preserves gauge coupling unification and a weakly coupled light Higgs while relaxing naturalness by placing squarks and sleptons at very high masses. Key proponents include Nima Arkani-Hamed, Savas Dimopoulos, Gian Francesco Giudice, and Matthew Strassler.

Introduction

Split SUSY arose as an alternative to low-energy natural supersymmetry in response to precision results from experiments such as LEP, Tevatron, and Large Hadron Collider. It maintains features familiar from Minimal Supersymmetric Standard Model constructions like gauge coupling unification and neutralino dark matter candidates while decoupling scalar superpartners, thereby reducing flavor-changing and CP-violating effects that troubled earlier proposals such as Gravity-mediated supersymmetry breaking scenarios. The paradigm connects to ideas from Grand Unified Theory model building and string-inspired constructions explored at institutions like CERN and SLAC National Accelerator Laboratory.

Theoretical Motivation and Framework

The theoretical motivation draws on tension between the hierarchy problem highlighted in analyses by Leonard Susskind and solutions like Supersymmetry championed by groups at Fermilab and DESY. Split SUSY accepts fine-tuning akin to anthropic arguments invoked in String landscape discussions and Weinberg's anthropic principle debates, while keeping fermionic superpartners light to preserve radiative corrections studied in Wilczek's and Georgi's work on unification. The framework is formulated with high-scale supersymmetry breaking generating scalar masses near a heavy scale referenced in Planck mass contexts, while gaugino and higgsino masses are protected by approximate symmetries similar to mechanisms considered in R-symmetry analyses by Edward Witten and Harvey collaborations. Renormalization group evolution equations used in the original proposals build on techniques from Wilczek and Gross–Wilczek computations of running couplings.

Particle Spectrum and Phenomenology

The characteristic spectrum contains heavy squarks and sleptons with masses possibly near scales discussed in Grand Unified Theory thresholds, and lighter gauginos and higgsinos with masses accessible at colliders such as LHC detectors like ATLAS and CMS. The Higgs boson mass prediction in Split SUSY leverages loop computations akin to those used in Higgs boson studies by the ATLAS and CMS collaborations and in theoretical analyses by Aleksandr Smirnov and Howard Haber. Collider signatures emphasize long-lived gluinos forming R-hadrons in searches performed by LHCb and cosmic-ray experiments analogous to analyses by Pierre Auger Observatory. Flavor and CP observables reference constraints from experiments at KEK and B-factories like Belle II, benefiting from decoupled scalar contributions, while precision electroweak fits connect to datasets from LEP and SLAC National Accelerator Laboratory.

Cosmology and Dark Matter Implications

Split SUSY provides dark matter candidates in the form of neutralinos, whose relic abundance analysis uses methods developed in WIMP studies and cosmological probes such as Planck (spacecraft) and WMAP. Thermal freeze-out, coannihilation, and nonthermal production scenarios reference frameworks employed in Griest & Seckel calculations and Affleck–Dine baryogenesis discussions. Indirect detection strategies parallel searches by Fermi Gamma-ray Space Telescope and AMS-02, while direct detection experiments like XENONnT and LUX-ZEPLIN set limits on scattering cross sections informed by nuclear matrix element work at Oak Ridge National Laboratory. Connections to early-universe processes examine impacts on reheating temperatures explored in studies at Princeton University and Institute for Advanced Study.

Experimental Constraints and Searches

Experimental constraints derive from null results in searches for superpartners at ATLAS, CMS, and previous colliders such as Tevatron (collider), with limits on gluino and electroweakino masses interpreted through Monte Carlo tools developed at CERN and the European Organization for Nuclear Research collaborations. Long-lived particle searches leverage detector subsystems and analysis methods refined in studies by CMS and ATLAS and techniques from IceCube for highly penetrating signatures. Precision flavor experiments at LHCb and Belle II provide bounds on rare decays influenced by virtual heavy scalars, while astrophysical surveys by Fermi Gamma-ray Space Telescope and VERITAS inform indirect dark matter constraints.

Variants and Extensions

Variants include models with partial splitting inspired by anomaly mediation proposals studied by Giudice, Luty, Murayama, Rattazzi and hybrids combining Split SUSY with Dirac gaugino frameworks explored in collaborations at Imperial College London and University of California, Berkeley. Other extensions incorporate extra gauge sectors or hidden valleys akin to ideas examined at SLAC National Accelerator Laboratory and CERN workshops, or embed splitting in string constructions discussed at conferences at KITP and Perimeter Institute. Connections to metastable supersymmetry breaking and ISS (Intriligator, Seiberg, Shih) mechanisms have been pursued by researchers at Rutgers University and Harvard University.

Open Questions and Future Directions

Open questions include explaining the origin and naturalness of the large scalar–fermion mass hierarchy, testable predictions for gluino lifetimes at future runs of the Large Hadron Collider and proposed colliders like the Future Circular Collider and International Linear Collider, and clarifying dark matter signals in next-generation detectors at SNOLAB and Gran Sasso National Laboratory. Ongoing theoretical work links Split SUSY to the string landscape and anthropic reasoning examined in debates at Perimeter Institute and Institute for Advanced Study, while upcoming data from ATLAS, CMS, and cosmological missions such as Euclid (spacecraft) will further constrain parameter space.

Category:Supersymmetry