Color–flavor locking explained

Color–flavor locking (CFL) is a phenomenon that is expected to occur in ultra-high-density strange matter, a form of quark matter. The quarks form Cooper pairs, whose color properties are correlated with their flavor properties in a one-to-one correspondence between three color pairs and three flavor pairs. According to the Standard Model of particle physics, the color-flavor-locked phase is the highest-density phase of three-flavor colored matter.^[1]

Color-flavor-locked Cooper pairing

If each quark is represented as

\psi ^{\alpha} _{i} , with color index \alpha taking values 1, 2, 3 corresponding to red, green, and blue, and flavor index i taking values 1, 2, 3 corresponding to up, down, and strange, then the color-flavor-locked pattern of Cooper pairing is ^[2] \langle \psi ^{\alpha} _{i} C \gamma _{5} \psi ^{\beta} _{j} \rangle \propto \delta ^{\beta} _{j} - \delta ^{\beta} _{i} = \epsilon ^{\alpha\beta} \epsilon _{ij}

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.
• It is a superfluid.
• It is an electromagnetic insulator, in which there is a "rotated" photon, containing a small admixture of one of the gluons.
• It has the same symmetries as sufficiently dense hyperonic 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.

See also

• Color superconductivity

Notes and References

1. M. Alford . K. Rajagopal . T. Schäfer . A. Schmitt . 2008 . Color superconductivity in dense quark matter . . 80 . 4. 1455–1515 . 10.1103/RevModPhys.80.1455 . 0709.4635. 2008RvMP...80.1455A . 14117263 .
2. M. Alford . K. Rajagopal . F. Wilczek . 1998 . QCD at Finite Baryon Density: Nucleon Droplets and Color Superconductivity . . 422 . 1–4 . 247–256 . 10.1016/S0370-2693(98)00051-3 . hep-ph/9711395. 1998PhLB..422..247A . 2831570 .