Nonoblique correction
Encyclopedia
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. There are three classes of radiative corrections to these processes: vacuum polarization
corrections, vertex corrections
, and box corrections. 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.
(The vacuum polarization corrections are referred to as oblique correction
s, 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.) 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. Another example is the anomalous magnetic dipole moment
.
In order to affect the nonoblique corrections, new particles must couple directly to the external fermions. Such couplings are expected to be suppressed in most cases, with one exception being the
vertex. Together with the oblique corrections, nonoblique corrections can be used to constrain models of new physics beyond the Standard Model
.
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...
, a nonoblique correction, also called a direct 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. Nonoblique 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 vertex and box corrections, which depend on the identity of the initial and final state fermions, are referred to as the non-oblique corrections.
(The vacuum polarization corrections are referred to as oblique correction
Oblique correction
In particle physics, an oblique correction refers to a particular type of radiative correction to the electroweak sector of the Standard Model. Oblique corrections are defined in four-fermion scattering processes, at the CERN LEP collider. There are three classes of radiative corrections to...
s, 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.) 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. Another example is the anomalous magnetic dipole moment
Anomalous magnetic dipole moment
In quantum electrodynamics, the anomalous magnetic moment of a particle is a contribution of effects of quantum mechanics, expressed by Feynman diagrams with loops, to the magnetic moment of that particle...
.
In order to affect the nonoblique corrections, new particles must couple directly to the external fermions. Such couplings are expected to be suppressed in most cases, with one exception being the
vertex. Together with the oblique corrections, nonoblique corrections can be used to constrain models of new physics beyond the Standard ModelBeyond 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...
.