These corrections are being studied at the CERN LEP collider.
The vertex and box corrections, which depend on the identity of the initial and final state fermions, are referred to as the non-oblique corrections.[why?]
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.
[clarification needed] An example of a vertex correction is the nonuniversality (flavor dependence) of the couplings of the quarks and leptons to the charged and neutral weak currents.
In order to affect the nonoblique corrections, particles must couple directly to the external fermions[why?].