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) over tilde) for large m((q) over tilde). 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) over bar(e<(nu)over tilde>(W) over tilde) and mixing matrices U-P,V-P, and includes all O(logm((q) over tilde)) corrections, while the other decouples for large m((q) over tilde). The form of the one-loop cross section then becomes physically transparent. Our formulation can he easily extended to other loops and processes. Numerically, we find significant corrections due to the effective t-channel coupling (g) over bar(e<(nu)over tilde>(W) over tilde), 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 reexamine previous studies of the determination of (g) over bar(e<(nu)over tilde>(W) over tilde) 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. [S0556-2821(98)03617-0].