The Cheshire Cat Bag Model: Color Anomaly and $η'$ Properties
We show that color can leak from a QCD bag if we allow for pseudoscalar isoscalar singlet ($η'$) coupling at the surface. To enforce total confinement of color an additional boundary term is suggested. New relations between the $η'$ mass and decay constant and the QCD gluon condensates are derived and compared with the empirical parameters.
hep-ph↗