The closure constraint for the hyperbolic tetrahedron as a Bianchi identity

The closure constraint is a central piece of the mathematics of loop quantum gravity. It encodes the gauge invariance of the spin network states of quantum geometry and provides them with a geometrical interpretation: each decorated vertex of a spin network is dual to a quantized polyhedron in $${\mathbb R}^{3}$$R3. For instance, a 4-valent vertex is interpreted as a tetrahedron determined by the four normal vectors of its faces. We develop a framework where the closure constraint is re-interpreted as a Bianchi identity, with the normals defined as holonomies around the polyhedron faces of a connection (constructed from the spinning geometry interpretation of twisted geometries). This allows us to define closure constraints for hyperbolic tetrahedra (living in the 3-hyperboloid of unit future-oriented spacelike vectors in $${\mathbb R}^{3,1}$$R3,1) in terms of normals living all in $$\mathrm {SU}(2)$$SU(2) or in $$\mathrm {SB}(2,{\mathbb C})$$SB(2,C). The latter fits perfectly with the classical phase space developed for q-deformed loop quantum gravity supposed to account for a non-vanishing cosmological constant $$\Lambda >0$$Λ>0. This allows the interpretation of q-deformed twisted geometries as actual discrete hyperbolic triangulations for 4d quantum gravity.