Oblique corrections are defined in four-fermion scattering processes, (e+ + e− → q + q ) at the CERN Large Electron–Positron Collider.
The vacuum polarization corrections are referred to as oblique corrections, since they only affect the mixing and propagation of the gauge bosons and they do not depend on which type of fermions appear in the initial or final states.
Any new particles charged under the electroweak gauge groups can contribute to oblique corrections.
Therefore, the oblique corrections can be used to constrain possible new physics beyond the Standard Model.
To affect the nonoblique corrections, on the other hand, the new particles must couple directly to the external fermions.