Gauge fixing and coBRST Original Research Article

It has previously been shown that a BRST quantization on an inner product space leads to physical states of the form |ph〉 = e[Q,ψ]|φ〉 where |φ〉 is either a trivially BRST invariant state which only depends on the matter variables, |φ〉1, or a solution of a Dirac quantization, |φ〉2. ψ is a corresponding fermionic gauge fixing operator, ψ1 or ψ2. We show here for abelian and nonabelian models that one may also choose a linear combination of ψ1 and ψ2 for both choices of |φ〉1, except for a discrete set of relations between the coefficients. A general form of the coBRST charge operator is also determined and shown to be equal to such a ψ for an allowed linear combination of ψ1 and ψ2. This means that the coBRST charge is always a good gauge fixing fermion.