Gauge invariance in the effective action and potential

The gauge dependence of the effective action GAMMA and potential V are studied in general gauge theories. Explicit expressions which manifest all the gauge dependences of GAMMA and V are obtained. From these equations, it is concluded that GAMMA (or V) has gauge-invariant values for any solution of the Euler-Lagrange equation deltaGAMMA/deltaphi = 0 (or partialV/partialphi = 0). Introduction of a certain concept about the categories of gauge conditions resolves the appearance of a gauge-dependent unphysical ''vacuum.'' Any gauge can be used to calculate GAMMA. A wide class of gauges are allowed for the effective potential V; for instance, in scalar QED the allowed gauges are -(1/2α)( partial A)2, -(1/2α)( partial A - upsilonPhi2)2 (where the direction of condensation is restricted to Phi1), the Coulomb gauge, and the axial gauge. In particular the R/sub xi/ gauge is also an allowed gauge