Spin-String Interaction in QCD Strings

I analyse the problem of introducing the spin of the quark and the antiquark in effective QCD strings from the point of view of the Wilson loop for a spin-half particle, or the Super Wilson loop. A string representation of the Super Wilson loop is obtained starting from an effective string representation of a Wilson Loop. The action obtained in this manner is invariant under a worldline supersymmetry and has a boundary term which contains the spin-string interaction. For rectangular loops the spin-string interaction vanishes. If an allowance is made for the finite thickness of the flux tube that is being modelled by a string then we obtain a spin-spin interaction which falls as the fifth power of the distance. Such a term was previously suggested by Kogut and Parisi in the context of a flux-tube model of confinement.