Instanton and higher-loop perturbative contributions to the QCD sum-rule analysis of pseudoscalar gluonium Original Research Article

Instanton effects and three-loop perturbative contributions are incorporated into QCD sum-rule analyses of pseudoscalar (JPC=0−+) gluonium. Gaussian sum-rules are shown to be superior to Laplace sum-rules in optimized predictions for pseudoscalar gluonium states in the presence of instanton contributions. The Gaussian sum-rule analysis yields a pseudoscalar mass of (2.65±0.33) GeV and width bounded by Γ<530 MeV. The Laplace sum-rules provide corroborating evidence in support of the ≈2.7 GeV mass scale.