Color–flavor locking
{{Short description|Phenomenon in high-density strange matter}}
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.
{{cite journal
|author1=M. Alford |author2=K. Rajagopal |author3=T. Schäfer |author4=A. Schmitt |year=2008
|title=Color superconductivity in dense quark matter
|journal=Reviews of Modern Physics
|volume=80 |issue= 4|pages=1455–1515
|doi= 10.1103/RevModPhys.80.1455
|arxiv=0709.4635
|bibcode = 2008RvMP...80.1455A |s2cid=14117263 }}
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, down, and strange, then the color-flavor-locked pattern of Cooper pairing is
{{cite journal
|author1=M. Alford |author2=K. Rajagopal |author3=F. Wilczek |year=1998
|title=QCD at Finite Baryon Density: Nucleon Droplets and Color Superconductivity
|journal=Physics Letters B
|volume=422 |issue=1–4 |pages=247–256
|doi=10.1016/S0370-2693(98)00051-3
|arxiv=hep-ph/9711395
|bibcode = 1998PhLB..422..247A |s2cid=2831570 }}
:
\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{{clarify|date=November 2012|there is no such thing as u–d–c SU(3) symmetry: these flavors have different *physical* properties (namely, mass, electric charge and weak interaction)}} 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.