In particle physics

Particle physics

Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

, an oblique correction refers to a particular type of radiative correction

Renormalization

In quantum field theory, the statistical mechanics of fields, and the theory of self-similar geometric structures, renormalization is any of a collection of techniques used to treat infinities arising in calculated quantities....

 to the electroweak sector of the Standard Model. Oblique corrections are defined in four-fermion

Fermion

In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....

 scattering processes, ( +  →  +  ) at the CERN

CERN

The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...

 LEP collider. There are three classes of radiative corrections to these processes: vacuum polarization

Vacuum polarization

In quantum field theory, and specifically quantum electrodynamics, vacuum polarization describes a process in which a background electromagnetic field produces virtual electron–positron pairs that change the distribution of charges and currents that generated the original electromagnetic...

 corrections, vertex corrections

Vertex function

In quantum electrodynamics, the vertex function describes the coupling between a photon and an electron beyond the leading order of perturbation theory...

, and box corrections. 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. (The vertex and box corrections, which depend on the identity of the initial and final state fermions, are called nonoblique correction

Nonoblique correction

In particle physics, a nonoblique correction, also called a direct correction, refers to a particular type of radiative correction to the electroweak sector of the Standard Model. Nonoblique corrections are defined in four-fermion scattering processes at the CERN LEP collider...

s.)

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

Beyond the Standard Model

Physics beyond the Standard Model refers to the theoretical developments needed to explain the deficiencies of the Standard Model, such as the origin of mass, the strong CP problem, neutrino oscillations, matter–antimatter asymmetry, and the nature of dark matter and dark energy...

. To affect the nonoblique corrections, on the other hand, the new particles must couple directly to the external fermions.

The oblique corrections are usually parameterized in terms of the Peskin-Takeuchi parameter

Peskin-Takeuchi parameter

In particle physics, the Peskin–Takeuchi parameters are a set of three measurable quantities, called S, T, and U, that parameterize potential new physics contributions to electroweak radiative corrections...

s S, T, and U.