Spinfoam tunneling of quantum geometries in angle variables

Abstract: Tunneling processes offer a promising path for finding signatures of quantum gravity. While tunneling of geometry has long been recognized in the literature, few detailed analyses have been carried out. We investigate covariant Loop Quantum Gravity transitions in the holonomy representation, which naturally encodes the extrinsic curvature of boundary states. We study these amplitudes within the simple framework of the Ponzano-Regge spinfoam model for three-dimensional Euclidean quantum gravity. Having identified the geometries that dominate the spinfoam path integral in the classically forbidden regime when it is formulated in terms of dihedral angles as boundary data, we argue that they correspond to tunneling processes. Finally, we characterize these non-classical geometries and show that their contributions to the spinfoam amplitude are exponentially suppressed in the semiclassical limit via analytic continuation of the discrete gravity action. This work sheds light on quantum black-to-white-hole transitions, in particular clarifying the origin of the exponential suppression of various quantum amplitudes.