Color–flavor locking

Color–flavor locking (CFL) 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 properties in a symmetric pattern. According to the standard model 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 $\psi^\alpha_i$, with color index α 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 ^[1]

$\langle \psi^\alpha_i C \gamma_5 \psi^\beta_j \rangle \propto \delta^\alpha_i\delta^\beta_j - \delta^\alpha_j\delta^\beta_i = \epsilon^{\alpha\beta A}\epsilon_{ij A}$

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.

Further reading

• M. Alford, K. Rajagopal, T. Schäfer, A. Schmitt (2008). "Color superconductivity in dense quark matter". Reviews of Modern Physics 80: 1455. arXiv:0709.4635. Bibcode 2008RvMP...80.1455A. doi:10.1103/RevModPhys.80.1455. 

References

1. ^ M. Alford, K. Rajagopal and F. Wilczek (1998). "QCD at Finite Baryon Density: Nucleon Droplets and Color Superconductivity". Physics Letters B 422: 247. arXiv:hep-ph/9711395. Bibcode 1998PhLB..422..247A. doi:10.1016/S0370-2693(98)00051-3.