Bound states and QCD

Understand

The similarities of hadrons and atoms motivate a study of the principles of QED bound states and of their applicability to QCD.

• The power series in $\alpha$ and $\log\alpha$ of the binding energy is reflected in the Fock expansion of the bound state in temporal gauge ($A^0=0$).
• Gauss' constraint on physical states fixes the gauge for time independent transformations and determines the instantaneous interaction within each Fock state.
• Positronium atoms generate a classical (dipole) electric field, whereas there can be no color octet gluon field for color singlet hadrons.