ABSTRACT
The quantisation of gauge theories in the path integral formalism requires more discussion, since the gauge condition seems to remove only one degree of freedom of the two that are eliminated in the Hamiltonian formulation. For non-Abelian gauge theories, because of the interaction of the ghost with the gauge field, ghosts can no longer be ignored. To have the ghosts eliminate the unphysical degrees of freedom, one should have the ‘masses’ of the ghosts coincide with the ‘masses’ of the unphysical degrees of freedom. The couplings of the ghost and unphysical fields to the physical fields should be related. The Haar measure coincides with the standard integration measure.
