“…We employ a systematic approach to the construction of interactions in gauge theories [19,20,21], based on the cohomological reformulation of Lagrangian BRST symmetry [22,23,24,25,26]. In this approach interactions result from the analysis of consistent deformations of the generator of the Lagrangian BRST symmetry (known as the solution of the master equation) by means of specific cohomological techniques, relying on local BRST cohomology [27,28]. The emerging deformations, and hence also the interactions, are constructed under the general hypotheses of locality, smoothness in the coupling constant, Poincaré invariance, Lorentz covariance, and derivative order assumption.…”