Comments On Torsion and MacDowell-Mansouri gravity
  Starting with the MacDowell-Mansouri formulation of gravity with a $SO(4,1)$ gauge group, we introduce new parameters into the action to include the non-dynamical Holst term, and the topological Nieh-Yan and Pontryagin classes. Then, we consider the new parameters as fields and analyze the solutions coming from their equations of motion. The new fields introduce torsional contributions to the theory that modify Einstein's equations. 
J. C. L\'opez-Dom\'inguez, J. E. Rosales-Quintero and M. Sabido
gr-qc