A General Treatment of Oblique Parameters

A re-examination is made of one-loop oblique electroweak corrections. General definitions are given of the oblique parameters without reference to any q 2 expansion scheme. The old oblique parameters S, T and U are defined as differences of gauge boson vacuum polarization Π functions and suffice for describing certain observable ratios on the Z peak and the ρ parameter at q 2 = 0. Regarding the new oblique parameters V, W and X, the first two are defined in terms of differences of Π functions as well as the wave function renormalization of the corresponding weak boson, and the third in terms of the difference of differences of two Π functions for γ - Z mixing. Explicit expressions for measurable quantities involving all six oblique parameters are given and experimental bounds are obtained on the latter, some for the first time. A review of these constraints suggests that the linear approximation of Peskin and Takeuchi is robust.