Principal Bundles, Connections and BRST Cohomology
  We review the elementary theory of gauge fields and the Becchi-Rouet-Stora- Tyutin symmetry in the context of differential geometry. We emphasize the topological nature of this symmetry and discuss a double Chevalley-Eilenberg complex for it. 
H. Garc\'ia-Compe\'an, J.M. L\'opez-Romero, M.A. Rodr\'iguez-Segura   and M. Socolovsky