BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Ilkka Mäkinen (University of Warsaw) DTSTART:20200430T183000Z DTEND:20200430T193000Z DTSTAMP:20260404T110825Z UID:PIQuantumGravity/1 DESCRIPTION:Title: Quantum-reduced loop gravity from the perspective of full LQG\nby Ilkka Mäkinen (University of Warsaw) as part of PI Quantum Gr avity\n\n\nAbstract\nQuantum-reduced loop gravity is a model of loop quant um gravity\, whose characteristic feature is the considerable simplicity o f its kinematical structure in comparison with that of full loop quantum g ravity. The model therefore provides an accessible testing ground for prob ing the physical implications of loop quantum gravity. In my talk I will g ive a brief introduction to quantum-reduced loop gravity\, and examine the relation between the quantum-reduced model and full loop quantum gravity. In particular\, I will focus on clarifying how the operators of the quant um reduced model are related to those of the full theory. I will show that despite their simplicity\, the operators of the quantum-reduced model are simply the operators of the full theory acting on states in the Hilbert s pace of the quantum-reduced model. In order to pass from the full theory o perators to the "reduced" operators\, one only has to keep in mind that th e states of the quantum-reduced model are labeled with large spins\, and d iscard terms which are of lower than leading order in j.\n LOCATION:https://stable.researchseminars.org/talk/PIQuantumGravity/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Simone Speziale (Aix Marseille University) DTSTART:20200514T190000Z DTEND:20200514T203000Z DTSTAMP:20260404T110825Z UID:PIQuantumGravity/2 DESCRIPTION:Title: Asymptotics of the EPRL model on arbitrary vertices\nb y Simone Speziale (Aix Marseille University) as part of PI Quantum Gravity \n\n\nAbstract\nWe introduce a new technique to study the critical point e quations of the eprl model. We show that it correctly reproduces the 4-sim plex asymptotics\, and how to apply it to an arbitrary vertex. We find tha t for general vertices\, the asymptotics can be linked to a Regge action f or polytopes\, but contain also more general geometries\, called conformal twisted geometries. We present explicit examples including the hypercube\ , and discuss implications.\n LOCATION:https://stable.researchseminars.org/talk/PIQuantumGravity/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Thomas Mertens (Universiteit Gent) DTSTART:20200521T183000Z DTEND:20200521T193000Z DTSTAMP:20260404T110825Z UID:PIQuantumGravity/3 DESCRIPTION:Title: Bulk observables in JT gravity\nby Thomas Mertens (Uni versiteit Gent) as part of PI Quantum Gravity\n\n\nAbstract\nUsing a defin ition of bulk diff-invariant observables\, we go into the bulk of 2d Jacki w-Teitelboim gravity. By mapping the computation to a Schwarzian path inte gral\, we study exact bulk correlation functions and discuss their physica l implications. We describe how the black hole thermal atmosphere gets mod ified by quantum gravitational corrections. Finally\, we will discuss how higher topological effects further modify the spectral density and detecto r response in the Unruh heat bath.\n LOCATION:https://stable.researchseminars.org/talk/PIQuantumGravity/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Yannick Herfray (Université Libre de Bruxelles) DTSTART:20200528T183000Z DTEND:20200528T193000Z DTSTAMP:20260404T110825Z UID:PIQuantumGravity/4 DESCRIPTION:Title: Conformal Geometry of Null Infinity\, including gravitatio nal waves\nby Yannick Herfray (Université Libre de Bruxelles) as part of PI Quantum Gravity\n\n\nAbstract\nSince the seminal work of Penrose\, it has been understood that conformal compactifications (or "asymptotic si mplicity") is the geometrical framework underlying Bondi-Sachs' descriptio n of asymptotically flat space-times as an asymptotic expansion. From this point of view the asymptotic boundary\, a.k.a "null-infinity"\, naturally is a conformal null (i.e degenerate) manifold. In particular\, "Weyl resc aling" of null-infinity should be understood as gauge transformations. As far as gravitational waves are concerned\, it has been well advertised by Ashtekar that if one work with a fixed representative for the conformal me tric\, gravitational radiations can be neatly parametrized as a choice of "equivalence class of metric-compatible connections". This nice intrinsic description however amounts to working in a fixed gauge and\, what is more \, the presence of equivalence class tend to make this point of view tedio us to work with.\n\nI will review these well-known facts and show how mode rn methods in conformal geometry (namely tractor calculus) can be adapted to the degenerate conformal geometry of null-infinity to encode the presen ce of gravitational waves in a completely geometrical (gauge invariant) wa y: Ashtekar's (equivalence class of) connections are proved to be in 1-1 c orrespondence with choices of (genuine) tractor connection\, gravitational radiation is invariantly described by the tractor curvature and the degen eracy of gravity vacua correspond to the degeneracy of flat tractor connec tions. The whole construction is fully geometrical and manifestly conforma lly invariant."\n LOCATION:https://stable.researchseminars.org/talk/PIQuantumGravity/4/ END:VEVENT END:VCALENDAR