The emergence of hadronic matter from interacting quarks and gluons

A characteristic of emergent phenomena is how novel and complex properties can emerge from apparently simple laws. Quantum ChromoDynamics (QCD) describes the interaction of quarks and gluons. The classical Lagrangian is remarkably simple.It has an SU(3) local gauge symmetry and the A_v^mu are the associated gauge fields (gluons).The quarks are fermions with fractional electrical charge. The only parameters in the theory are the coupling constant g_s, which describes the self-interaction of the gluons, and the masses of the quarks, m_f. The gluons are massless. The Lagrangian has chiral symmetry, which transforms quarks with left-handed symmetry into right-handed.Frank Wilczek states that QCD "is conceptually simple. Its realisation in nature, however, is usually very complex. But not always."Hadronic matter (nucleons and mesons) has properties that are qualitatively different from its components (interacting quarks and gluons). In other words, it is emergent.In hadronic matter, there…