BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Panagiotis Charalambous (SISSA\, Trieste and INFN\, Trieste) DTSTART:20251007T090000Z DTEND:20251007T100000Z DTSTAMP:20260423T024827Z UID:NKUA-HEP/41 DESCRIPTION:Title: Null infinity at the edge of a black hole\nby Panagiotis Charalambou s (SISSA\, Trieste and INFN\, Trieste) as part of NKUA HEP Seminars\n\nLec ture held in online.\n\nAbstract\nNull hypersurfaces are lightlike surface s that naturally emerge when asking questions like “what is an asymptoti cally flat spacetime?” or “what is a black hole?”. This gives rise t o the concepts of “null infinities” and “event horizons”. In this talk\, I will highlight the observation that all spacetimes that are asymp totically flat near null infinity can be mapped through spatial inversions onto the geometry near an extremal\, non-expanding and non-rotating horiz on located at a finite distance. This mapping is conformal\, ensuring the dissimilar physics on each type of null surface\, but also emphasizing the ir similarities. Typically\, the conformally related asymptotic geometries do not reside in the same spacetime. When they do\, however\, the finite- distance horizon is a true black hole event horizon\, and the correspondin g spatial inversions become conformal isometries of the spacetime that exc hange the two null surfaces. The prototypical example of this situation is the four-dimensional extremal Reissner-Nordström black hole\, equipped w ith the characteristic Couch-Torrence inversion conformal isometry. This c orrespondence then enforces matching conditions between near-horizon and n ear–null-infinity data\, leading\, in particular\, to the identification between infinite towers of conserved quantities: the near-horizon Aretaki s constants and the near–null-infinity Newman-Penrose constants. I will also present hints of a broader relationship between disconnected null hyp ersurfaces under less restrictive boundary conditions\, extending beyond e xtremal\, static horizons to include rotating or even non-extremal cases.\ n LOCATION:https://researchseminars.org/talk/NKUA-HEP/41/ END:VEVENT END:VCALENDAR