BRS SYMMETRY FOR YANG-MILLS THEORY WITH EXACT RENORMALIZATION-GROUP

In the exact renormalization-group (RG) flow in the infrared cutoff Lambda one needs boundary conditions, In a previous paper on SU(2) Yang-Mills theory we proposed to use the nine physical relevant couplings of the effective action as boundary conditions at the physical point Lambda = 0 (these couplings are defined at some non-vanishing subtraction point mu not equal 0). In this paper we show perturbatively that it is possible to appropriately fix these couplings in such a way that the full set of Slavnov-Taylor (ST) identities are satisfied. Three couplings are given by the vector and ghost wave-function normalization and the three-vector coupling at the subtraction point; three of the remaining six are vanishing (e.g. the vector mass) and the others are expressed by irrelevant vertices evaluated at the subtraction point. We follow the method used by Becchi to prove ST identities in the RG framework. There the boundary conditions are given at a non-physical point Lambda = Lambda' not equal 0, so that one avoids the need of a non-vanishing subtraction point.