A variational approach to the QCD wavefunctional: Calculation of the QCD $\beta$-function

The beta-function is calculated for an SU(N) Yang-Mills theory from an ansatz for the vacuum wavefunctional. Direct comparison is made with the results of calculations of the beta-function of QCD. In both cases the theories are asymptotically free. The only difference being in the numerical coefficient of the beta-function, which is found to be -4 from the ansatz and -4+1/3 from other QCD calculations. This is because, due to the constraint of Gauss' law applied to the wavefunctional, transverse gluons (which contribute the 1/3) are omitted. The renormalisation procedure is understood in terms of `tadpole' and `horse-shoe' Feynman diagrams which must be interpreted with a non-local propagator