Center vortices are line-like topological defects that exist in the vacuum of Yang–Mills theory and QCD.
There is evidence in lattice simulations that they play an important role in the confinement of quarks.
In the case of SU(N) gauge theories, the center consists of the constant matrices: where I is the unit matrix.
This means that, if quarks are free (like in the deconfined phase), the center symmetry will be broken.
[2] At low temperatures (where there is confinement) vortices form large, complex clusters and percolate through space.
At higher temperatures (above the deconfinement phase transition) vortices form small loops.
[3] At the other hand, the string tension remains approximately unchanged when removing everything except for the center vortices.
Aside from this it has also been shown in simulations that the vortices have a finite density in the continuum limit (meaning they are not a lattice artifact, but they do exist in reality), and that they are also linked with chiral symmetry breaking and topological charge.
Also G2 gauge theory does not have a long-range string tension, which is consistent with the center vortex picture.