Gowrisankar Sreeram | Searcharxiv

arXiv2026

Closing the Loop: from EPRL-FK spinfoams to Regge dynamics

The EPRL-FK spinfoam model in its semiclassical regime at fixed discretization faces a big limitation: its dominant configurations describe only flat geometries. We ask what additional condition is needed for the variational principle to reproduce the equations of motion of Regge calculus, the standard discretization of General Relativity. We recast the EPRL-FK model in wedge-holonomy variables and identify geometric closure as the missing condition. We prove that imposing geometric closure as an additional constraint alongside local flatness allows us to reconstruct curved geometries. On a regular, nondegenerate Lorentzian branch with spacelike tetrahedra, modulo gauge, they define a constraint surface equivalent to the space of length-Regge geometries. The wedge action restricted to this surface becomes the Regge action, and its tangent variations yield the length-Regge equations. Finally, we propose a way to implement geometric closure directly in the spinfoam amplitude. With this additional constraint, the EPRL-FK model is therefore equivalent to Regge calculus in its semiclassical regime.

gr-qc↗

arXiv2025

Spinfoam tunneling of quantum geometries in angle variables

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 in covariant Loop Quantum Gravity have been carried out. We investigate spinfoam transitions in the holonomy representation, which naturally encodes the extrinsic curvature of boundary states. To reduce technical complications to a minimum, we study these amplitudes within the simple framework of the Ponzano-Regge spinfoam model for three-dimensional Euclidean quantum gravity. We identify the geometries dominating the spinfoam path integral in the classically forbidden regime when formulated in terms of dihedral angles as boundary data. 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. We argue that they satisfy all the desired properties of tunneling processes. We also shed light on quantum black-to-white-hole transitions, in particular clarifying the origin of the exponential suppression of various quantum amplitudes, while at the same time laying the basis for a future complete calculation of the amplitude in covariant Loop Quantum Gravity.

gr-qc↗