Editing Quantum chromodynamics (section)

===Some definitions===
{{unsolved|physics|QCD in the non-[[perturbation theory (quantum mechanics)|perturbative]] regime:
*'''[[Color confinement|Confinement]]''': the equations of QCD remain unsolved at [[energy scale]]s relevant for describing [[atomic nucleus|atomic nuclei]]. How does QCD give rise to the physics of nuclei and nuclear constituents?
*'''[[QCD matter|Quark matter]]''': the equations of QCD predict that a [[quark–gluon plasma|plasma (or soup) of quarks and gluons]] should be formed at high temperature and density. What are the properties of this [[phase of matter]]?}}<!-- please don't insert a line feed here, without checking to ensure that spacing remains as it should -->
Every field theory of [[particle physics]] is based on certain symmetries of nature whose existence is deduced from observations. These can be
*[[Local symmetry|local symmetries]], which are the symmetries that act independently at each point in [[spacetime]]. Each such symmetry is the basis of a [[gauge theory]] and requires the introduction of its own [[gauge boson]]s.
*[[Global symmetry|global symmetries]], which are symmetries whose operations must be simultaneously applied to all points of spacetime.

QCD is a non-abelian gauge theory (or [[Yang–Mills theory]]) of the [[special unitary group|SU(3)]] gauge group obtained by taking the [[color charge]] to define a local symmetry.

Since the strong interaction does not discriminate between different flavors of quark, QCD has approximate '''flavor symmetry''', which is broken by the differing masses of the quarks.

There are additional global symmetries whose definitions require the notion of [[chirality (physics)|chirality]], discrimination between left and right-handed. If the [[Spin (physics)|spin]] of a particle has a positive [[projection (linear algebra)|projection]] on its direction of motion then it is called right-handed; otherwise, it is left-handed.  Chirality and handedness are not the same, but become approximately equivalent at high energies.
*'''Chiral''' symmetries involve independent transformations of these two types of particle.
*'''Vector''' symmetries (also called diagonal symmetries) mean the same transformation is applied on the two chiralities.
*'''Axial''' symmetries are those in which one transformation is applied on left-handed particles and the inverse on the right-handed particles.