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 $alpha$ taking values 1,2,3 correspondingto red, green, and blue, and flavor index $i$ takingvalues 1,2,3 corresponding to up, down, and strange, then the color-flavor lockedpattern of Cooper pairing is [M. Alford, K. Rajagopal and F. Wilczek, "QCD at Finite Baryon Density: Nucleon Droplets and Color Superconductivity" [http://www.arXiv.org/abs/hep-ph/9711395 arxiv:hep-ph/9711395] ,published as Phys. Lett. B422, 247 (1998).]

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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, "Color superconductivity in dense quark matter", [http://arxiv.org/abs/0709.4635 arxiv:0709.4635] , to be published in Reviews of Modern Physics.

References