Supersymmetric contributions to muon g−2 and the electroweak precision measurements

In view of the recent measurement of the muon g−2 and finalization of the LEP electroweak data, we reexamine all the new particle contributions to those observables in the MSSM. The SM fits the latest electroweak data excellently with the observed top-quark mass and the Higgs-boson mass of around 100 GeV, and so does the MSSM in the decoupling limit. The MSSM gives a slightly better fit to the data than the SM (Δχ2min∼−2) when relatively light left-handed sleptons of mass ∼200 GeV and a light chargino of mixed higgsino–wino character (μ/M2∼1) with mass ∼100 GeV coexist. The improvement in the fit diminishes quickly for wino- or higgsino-dominant charginos, for heavier charginos, and for lighter sleptons. We find that the MSSM contributions to the muon g−2 is most efficient when the light chargino has a mixed character. If tanβ<10, the set of a light mixed chargino and light sleptons that is favored by the electroweak data is also favored by the g−2 data for μ>0. Models with light gauginos (μ/M2>10) or light higgsinos (μ/M2<0.1) give significant contributions to muon g−2 only for large tanβ (≳15).