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Radiative Corrections to a Supersymmetric Relation: A New Approach


Recently it has been realized that the production and decay processes of charginos, neutralinos, and sleptons receive corrections which grow like $\log m_{\tilde q}$ for large $m_{\tilde q}$. In this paper we calculate the chargino pair production cross section at $e^+e^-$ colliders with quark/squark loop corrections. We introduce a novel formulation, where the one-loop amplitude is reorganized into two parts. One part is expressed in terms of the ``effective'' chargino coupling \gbar\ and mixing matrices $U^P,\ V^P$, and includes all ${\cal O}(\log m_{\tilde q})$ corrections, while the other decouples for large $m_{\tilde q}$. The form of the one-loop cross section then becomes physically transparent. Our formulation can be easily extended to other loops and processes. Numerically, we find significant corrections due to the effective $t$-channel coupling \gbar, for gaugino-like charginos. In the mixed region, where the chargino has large gaugino and Higgsino components, the corrections due to ($U^P$, $V^P$) are also significant. Our numerical results disagree with a previous calculation. We revisit previous studies of the determination of \gbar\ through the measurement of the chargino production cross section. We point out that a previous study, which claimed that the measurement suffers large systematic errors, was performed at a ``pessimistic'' point in MSSM parameter space. We provide reasons why the systematic errors are not a limiting factor for generic parameter choices.

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