The Ponzano-Regge model and Reidemeister torsion
  The Ponzano-Regge model of three-dimensional quantum gravity is well-defined when the observables satisfy a certain condition involving the twisted cohomology. In this case, the partition function is defined in terms of the Reidemeister torsion. Some consequences for the special cases of planar graphs and knots are given. 
John W. Barrett, Ileana Naish-Guzman