Effective operator contributions to the oblique parameters

Abstract We present a model and process independent study of the contributions from non-Standard Model physics to the oblique parameters S , T and U . We show that within an effective lagrangian parameterization the expressions for the oblique parameters in terms of observables are consistent, while those in terms of the vector-boson vacuum polarization tensors are ambiguous. We obtain the constraints on the scale of new physics derived from current data on S , T and U and note that deviations in U from its Standard Model value would favor a scenario where the underlying physics does not decouple.