Divergences and Orientation in Spinfoams
  We suggest that large radiative corrections appearing in the spinfoam framework might be tied to the implicit sum over orientations. Specifically, we show that in a suitably simplified context the characteristic "spike" divergence of the Ponzano-Regge model disappears when restricting the theory to just one of the two orientations appearing in the asymptotic limit of the vertex amplitude. 
Marios Christodoulou, Miklos L{\aa}ngvik, Aldo Riello, Christian   R\"oken, Carlo Rovelli
gr-qc