Two-loop versus new physics effects on oblique parameters

Abstract

We utilize the recent calculation of the dominant two-loop radiative corrections to electroweak parameters to investigate higher order effects on the standard model predictions for the oblique parameters S, T and U. The variations of these contributions over a wide range of top quark and Higgs boson masses are investigated. The magnitude of two-loop effects is often greater than that of certain new physics scenarios beyond the standard model which have been considered in this context, and therefore must be taken into account first. However, two-loop effects never move both S and T simultaneously towad more negative values and therefore do not reduce the tantalizing 1 to 1.5σ discrepancy of the present data with the standard model.