Simone Speziale

Sep 11, 2024 | mdpi.com | Abhay Ashtekar |Simone Speziale

1. IntroductionIt is a pleasure to write this article in honor of Jorge Pullin on the occasion of his 60th birthday. Jorge has made important contributions to loop quantum gravity and classical general relativity over the years and, rather astonishingly, he is currently engaged in experimental work at the LIGO Livingston facility.

Aug 26, 2024 | link.aps.org | Antoine Rignon-Bret |Aix Marseille Université |Université de Toulon |Simone Speziale

We show that when the Wald-Zoupas prescription is implemented, the resulting charges realize the Bondi-Van der Burg–Metzner-Sachs (BMS) symmetry algebra without any 2-cocycle nor central extension, at any cut of future null infinity. We refine the covariance prescription for application to the charge aspects, and introduce a new aspect for Geroch’s supermomentum with better covariance properties.

Aug 26, 2024 | link.aps.org | Abhay Ashtekar |Simone Speziale |Aix Marseille Université |Université de Toulon

Null infinity, I+, arises as a boundary of the Penrose conformal completion (M^,g^ab) of an asymptotically flat physical space-time (M,gab). We first note that I+ is a weakly isolated horizon (WIH) in (M^,g^ab), and then show that its familiar geometric properties can be derived from the general WIH framework. This seems quite surprising because physics associated with black hole (and cosmological) WIHs Δ is very different from that extracted at I+.