Color–flavor locking is a phenomenon that is expected to occur in ultra-high-density quark matter. The quarks form Cooper pairs, whose color properties are correlated with their flavor

Flavour (particle physics)

In particle physics, flavour or flavor is a quantum number of elementary particles. In quantum chromodynamics, flavour is a global symmetry...

 properties in a symmetric pattern. According to the standard model

Standard Model

The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...

 of particle physics, the color-flavor-locked phase is the highest-density phase of three-flavor matter.

Color-flavor-locked Cooper pairing

If each quark is represented as , with color index taking values 1,2,3 corresponding to red, green, and blue, and flavor index taking values 1,2,3 corresponding to up

Up quark

The up quark or u quark is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons and protons of atomic nuclei...

, down

Down quark

The down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the up quark, forms the neutrons and protons of atomic nuclei...

, and strange

Strange quark

The strange quark or s quark is the third-lightest of all quarks, a type of elementary particle. Strange quarks are found in hadrons, which are subatomic particles. Example of hadrons containing strange quarks include kaons , strange D mesons , Sigma baryons , and other strange particles...

, then the color-flavor locked pattern of Cooper pairing is


This means that a Cooper pair of an up quark and a down quark must have colors red and green, and so on. This pairing pattern is special because it leaves a large unbroken symmetry group.

Physical properties

The CFL phase has several remarkable properties.

• It breaks chiral symmetry
  Chiral symmetry
  In quantum field theory, chiral symmetry is a possible symmetry of the Lagrangian under which the left-handed and right-handed parts of Dirac fields transform independently...
  
  .
• It is a superfluid
  Superfluid
  Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...
  
  .
• It is an electromagnetic insulator, in which there is a "rotated" photon
  Photon
  In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
  
  , containing a small admixture of one of the gluon
  Gluon
  Gluons are elementary particles which act as the exchange particles for the color force between quarks, analogous to the exchange of photons in the electromagnetic force between two charged particles....
  
  s.
• It has the same symmetries as sufficiently dense hyperon
  Hyperon
  In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm quarks or bottom quarks.-Properties and behavior of hyperons:...
  
  ic matter

.
There are several variants of the CFL phase, representing distortions of the pairing structure in response to external stresses such as a difference between the mass of the strange quark and the mass of the up and down quarks.