Entropies for gravitational systems from simplicial Lorentzian path integrals

          @misc{ pirsa_PIRSA:25100186,
            doi = {10.48660/25100186},
            url = {https://pirsa.org/25100186},
            author = {Padua Arg{\"u}elles, Jos{\'e} de Jes{\'u}s},
            keywords = {},
            language = {en},
            title = {Entropies for gravitational systems from simplicial Lorentzian path integrals},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {oct},
            note = {PIRSA:25100186 see, \url{https://pirsa.org}}
          }
          

Abstract

Recent advances have argued how gravitational entropies can be computed directly from Lorentzian path integrals, avoiding the problems of Euclidean methods associated with the conformal factor problem that makes a path integral over Euclidean geometries manifestly ill defined. In particular, the de Sitter horizon entropy can be recovered from a real-time path integral that computes the dimension of the Hilbert space associated with a spatial ball. Similarly, the swap entropy of an evaporating black hole (central to the replica paradigm resolution of the black hole information paradox) can be computed in this way. Quantum Regge Calculus, a lattice-like approach to quantum gravity, enables concrete realizations of these scenarios, providing insights beyond continuum methods. This perspective clarifies aspects of gravitational path integrals and may have implications for approaches such as causal dynamical triangulations and spin foams, where Regge-like formulations play a fundamental role.