New spinfoam vertex for quantum gravity

@article{Livine2007NewSV,
  title={New spinfoam vertex for quantum gravity},
  author={Etera R. Livine and Simone Speziale},
  journal={Physical Review D},
  year={2007},
  volume={76},
  pages={084028}
}
We introduce a new spinfoam vertex to be used in models of 4d quantum gravity based on SU(2) and SO(4) BF theory plus constraints. It can be seen as the conventional vertex of SU(2) BF theory, the 15j symbol, in a particular basis constructed using SU(2) coherent states. This basis makes the geometric interpretation of the variables transparent: they are the vectors normal to the triangles within each tetrahedron. We study the condition under which these states can be considered semiclassical… 
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