Chiral effective theory of strong interactions

A review of chiral effective theory (CET) is presented. CET is based on quantum chromodynamics (QCD) and describes strong interaction processes at low energies. It is proved that CET arises as a consequence of the spontaneous violation of chiral symmetry in QCD — the appearance of chiral-symmetry-violating vacuum condensates. The Goldstone theorem is proved for the case of QCD, and the existence of the octet of massless Goldstone bosons (π, K, η) is demonstrated in the limit of massless u, d and s quarks (or the existence of the triplet of massless pions in the limit m_u, m_d →0). It is shown that the same phenomenon — the appearance of quark condensate in QCD — which is responsible for the Goldstone bosons also gives rise to chiral-symmetry-violating massive baryons. The general form of the CET Lagrangian is derived. Examples of higher order corrections to tree diagrams in CET are considered. The Wess–Zumino term (i.e., the p⁴ term in the CET Lagrangian) is given. Low energy sum rules are presented. QCD and CET at finite temperature are discussed. In the CET framework, the T² correction to quark condensate in QCD is calculated at finite temperature, and results including higher order temperature corrections are presented. These results indicate on a phase transition to occur at T ≈ 150 – 200 MeV in QCD. The mixing of current correlators in order of T² is proved.