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 logm_ ̃ \~q for large m_ ̃ \~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 g_e ̃ \~ν ̃ \~W and mixing matrices UP,VP, and includes all O(logm_ ̃ \~q) corrections, while the other decouples for large m_ ̃ \~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 g_e ̃ \~ν ̃ \~W, for gaugino-like charginos. In the mixed region, where the chargino has large gaugino and Higgsino components, the corrections due to (UP,VP) are also significant. Our numerical results disagree with a previous calculation. We reexamine previous studies of the determination of g_e ̃ \~ν ̃ \~W 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.