A Note on B-observables in Ponzano-Regge 3d Quantum Gravity
  We study the insertion and value of metric observables in the (discrete) path integral formulation of the Ponzano-Regge spinfoam model for 3d quantum gravity. In particular, we discuss the length spectrum and the relation between insertion of such B-observables and gauge fixing in the path integral. 
Etera R. Livine, James P. Ryan