The Minimal Supersymmetric Model without a mu term
Ann E. Nelson, Nuria Rius, Veronica Sanz, Mithat Unsal
TL;DR
Problem: the MSSM requires a μ parameter that is of order the SUSY-breaking scale, which is unnatural. Approach: formulate the μ-free MSSM, the not-μ SSM, by extending MSSM with a minimal SU(2) triplet and enforcing an approximate U(1)_R symmetry so that all mass terms arise from SUSY breaking or EWSB and tanβ is large. Key results: this framework removes the μ term, yields an upper bound on the lightest chargino mass, m_chi1pm ≤ sqrt(2) m_W ≈ 114 GeV, and allows gauge- or gravity-mediated SUSY breaking without reintroducing a μ problem while avoiding the MSSM Higgs bound. Significance: the model suppresses SUSY contributions to g-2, b→sγ, and proton decay, can accommodate gauge coupling unification with a low messenger scale, and makes collider-testable predictions such as two light charginos near 104–120 GeV and a heavier state around 270 GeV.
Abstract
We propose a supersymmetric extension of the standard model which is a realistic alternative to the MSSM, and which has several advantages. No ``mu'' supersymmetric Higgs/Higgsino mass parameter is needed for sufficiently heavy charginos. An approximate U(1) R symmetry naturally guarantees that tan beta is large, explaining the top/bottom quark mass hierarchy. This symmetry also suppresses supersymmetric contributions to anomalous magnetic moments, b to s gamma, and proton decay, and these processes place no lower bounds on superpartner masses, even at large tan beta. The soft supersymmetry breaking mass parameters can easily be obtained from either gauge or Planck scale mediation, without the usual mu problem. Unlike in the MSSM, there are significant upper bounds on the masses of superpartners, including an upper bound of 114 GeV on the mass of the lightest chargino. However the MSSM bound on the lightest Higgs mass does not apply.