On the Relation Between Quadratic and Linear Curvature Lagrangians in   Poincar\'e Gauge Gravity
  We discuss the choice of the Lagrangian in the Poincar\'e gauge theory of gravity. Drawing analogies to earlier de Sitter gauge models, we point out the possibility of deriving the Einstein-Cartan Lagrangian {\it without} cosmological term from a {\it modified} quadratic curvature invariant of {\it topological} type. 
Yuri N. Obukhov and Friedrich W. Hehl