Condensates Break Chiral Symmetry

In the physical vacuum of QCD, the energy density of light-quark fields strongly coupled to slowly varying gluon fields can be negative. The states that drive this energy density lowest are condensates of pairs of quarks and antiquarks of nearly opposite momenta. These quark-antiquark condensates break chiral symmetry. They may also affect other features of hadronic physics, such as the range of the strong force and the confinement of color.