Relation between Yang–Mills glueballs and QCD glueballs

Determine how, or whether, glueball states in full QCD with dynamical quarks are related to the glueball states of quarkless SU(3) Yang–Mills theory, in order to assess the rigor of phenomenological interpretations based on Yang–Mills calculations.

Background

Many theoretical and phenomenological expectations for glueballs are based on the well-established spectrum calculated in quarkless SU(3) Yang–Mills theory. The chapter notes that radiative charmonium-decay calculations and experimental interpretations often use these Yang–Mills results, even though physical QCD contains light quarks and allows mixing and hadronic decays. Clarifying the correspondence between the two theories is therefore necessary before Yang–Mills predictions can be reliably used to identify glueballs in experiment.