“…To study the renormalizability of the action (2.7), the first step is to introduce some external sources in order to control the non-linear nature of the BRST transformations and other possible non-linear symmetries. The required BRST doublets are [8] sτ a µ = Ω a µ , sΩ a µ = 0 , sE a = L a , sL a = 0 , sΛ a µν = K a µν , sK a µν = 0 ,…”