BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Geoffrey Compère DTSTART:20220314T130000Z DTEND:20220314T134000Z DTSTAMP:20260422T212608Z UID:PhysBound/1 DESCRIPTION:Title: Tails and memories: Monsieur Théophile de Donder meets Sir Hermann Bond i\nby Geoffrey Compère as part of Physics @ Boundaries Workshop\n\n\n Abstract\nThe multipolar post-Minkowskian formalism describes the external gravitational field outside sources such as a compact binary merger. In t his formalism\, the metric is expanded in harmonic gauge\, also known as d e Donder gauge. In radiation zone\, at length scales above the gravitation al wave typical wavelength\, the metric is best studied in Bondi or Newman -Unti gauge where an infinite set of flux-balance laws describe much physi cs of interest. In this talk\, I will describe how to transfer known resul ts from de Donder gauge to Bondi gauge\, first at linear order and then at quadratic order in the post-Minkowskian expansion. I will discuss the tai l and memory effects from this point of view\, as well the description of recently defined $w(1+\\infty)$ charges in terms of canonical multipole mo ments.\n LOCATION:https://researchseminars.org/talk/PhysBound/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Laura Donnay DTSTART:20220314T135000Z DTEND:20220314T143000Z DTSTAMP:20260422T212608Z UID:PhysBound/2 DESCRIPTION:Title: A Carrollian Perspective on Celestial Holography\nby Laura Donnay as part of Physics @ Boundaries Workshop\n\n\nAbstract\nA Carrollian Perspec tive on Celestial Holography\nAbstract: In this talk\, we will present a h olographic description of gravity in 4d asymptotically flat spacetime in t erms of a 3d sourced conformal Carrollian field theory. The external sourc es encode the leaks of gravitational radiation at null infinity. The Ward identities of this theory are shown to reproduce those of the 2d celestial CFT after relating Carrollian to celestial operators. This suggests a new set of interplays between gravity in asymptotically flat spacetime\, sour ced conformal Carrollian field theory and celestial CFT.\n LOCATION:https://researchseminars.org/talk/PhysBound/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Ted Jacobson(Substituted by Rodrigo Andrade e Silva) DTSTART:20220314T144000Z DTEND:20220314T152000Z DTSTAMP:20260422T212608Z UID:PhysBound/3 DESCRIPTION:Title: Causal diamonds in 2+1 dimensional quantum gravity\nby Ted Jacobson( Substituted by Rodrigo Andrade e Silva) as part of Physics @ Boundaries Wo rkshop\n\n\nAbstract\nWe identify the reduced phase space of causal diamon ds with fixed edge\nlength in pure 2+1 dimensional gravity with a negative cosmological constant\,\nwhich turns out to be the cotangent bundle of th e homogeneous space\n$Diff^+(S^1)/PSL(2\,R)$. Isham’s group theoretic qu antization scheme is applied to\nthis nonlinear phase space. We find that the twist of the boundary curve (which\nis also the ``spin” of the diamo nd) is quantized in integer or half-integer\nmultiples of the ratio of the Planck length to the diamond edge length.\n LOCATION:https://researchseminars.org/talk/PhysBound/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Marc Geiller DTSTART:20220315T130000Z DTEND:20220315T134000Z DTSTAMP:20260422T212608Z UID:PhysBound/4 DESCRIPTION:Title: The partial Bondi gauge\nby Marc Geiller as part of Physics @ Bounda ries Workshop\n\n\nAbstract\nI will present an analysis of 4d gravity in a partial Bondi gauge\, where only three conditions instead of the usual fo ur are imposed on the metric. The so-called determinant condition usually imposed on the angular metric is in particular dropped. This partial gauge still enables to construct a solution space\, which can accommodate an ar bitrary cosmological constant\, boundary sources\, the ''trace of the shea r''\, and polyhomogeneous terms. After presenting this solution space I wi ll discuss the asymptotic symmetries. The partial gauge is in particular a dapted to treating in a unified manner and contrasting the celebrated Bond i-Sachs gauge\, and the Newman-Unti gauge\, which we find to be inequivale nt. This latter does indeed enable to access a new asymptotic symmetry. Th is construction generalizes previous work in 3d gravity\, which I will als o present as further motivation for the 4d extension.\n LOCATION:https://researchseminars.org/talk/PhysBound/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Vahid Taghiloo DTSTART:20220315T135000Z DTEND:20220315T143000Z DTSTAMP:20260422T212608Z UID:PhysBound/5 DESCRIPTION:Title: Null Surface Thermodynamics\nby Vahid Taghiloo as part of Physics @ Boundaries Workshop\n\n\nAbstract\nIn this talk\, I'm going to formulate t he D-dimensional Einstein gravity in presence of a codimension one null bo undary. As we will see in addition to the bulk degrees of freedom that pro pagate into the bulk we also have to account for the boundary degrees of f reedom that reside at the boundary. A suitable way to label these boundary degrees of freedom is using the surface charges associated with large dif feomorphisms. Surprisingly\, we will also observe these boundary degrees o f freedom describe a thermodynamic system with local laws of thermodynamic s. This thermodynamical system is generally an open system and can be clos ed only when there is no flux of gravitons through the null surface. Local laws of thermodynamics are a manifestation of diffeomorphism invariance o f the theory at the boundary and account for the dynamics of the part of s pacetime behind the boundary. Our analysis extends the usual black hole th ermodynamics to a universal feature of any area element on a generic null surface in a generic diffeomorphism invariant theory of gravity.\n LOCATION:https://researchseminars.org/talk/PhysBound/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrew Strominger DTSTART:20220315T144000Z DTEND:20220315T152000Z DTSTAMP:20260422T212608Z UID:PhysBound/6 DESCRIPTION:Title: The Universe as a Quantum Encoder\nby Andrew Strominger as part of P hysics @ Boundaries Workshop\n\n\nAbstract\nArguments are given that time evolution in an expanding universe is a non-unitary isometry.\n LOCATION:https://researchseminars.org/talk/PhysBound/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Grumiller DTSTART:20220316T130000Z DTEND:20220316T134000Z DTSTAMP:20260422T212608Z UID:PhysBound/7 DESCRIPTION:Title: Near Horizon Symmetries\nby Daniel Grumiller as part of Physics @ Bo undaries Workshop\n\n\nAbstract\nPhysics at null boundaries is relevant in flat space holography and for black holes. I focus on the latter\, revie wing near horizon symmetries and their implications for soft hair\, black hole entropy\, phase space \nslicings\, and memory effects.\n LOCATION:https://researchseminars.org/talk/PhysBound/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert Leigh DTSTART:20220316T135000Z DTEND:20220316T143000Z DTSTAMP:20260422T212608Z UID:PhysBound/8 DESCRIPTION:Title: Symmetries of Diff-invariant theories\nby Robert Leigh as part of Ph ysics @ Boundaries Workshop\n\n\nAbstract\nIn this talk\, I will consider a universal group of symmetries that are associated to embedded surfaces i n a classical spacetime. In the codimension-2 case\, we refer to these sur faces as corners\, and the symmetry as the extended corner symmetry. In th e context of the Einstein-Hilbert theory\, we show that the Noether charge s supported by such a corner coincide precisely with the extended corner s ymmetry. The inclusion of the embedding map into the phase space of the th eory allows for a calculation of the algebra of charges. We then show that within the covariant phase space formalism\, there is a precise way of ex tending the phase space such that all charges are integrable and associate d with Hamiltonian vector fields on field space. The algebra of charges is then consistently represented in terms of the Poisson brackets of this ex tended phase space theory. This resolves an old conundrum in gravity\, sep arating the notion of non-integrability from non-conservation. Finally\, w e discuss some recent work employing the orbit method which relates corner s to certain symplectic reductions. This gives an entirely group theoretic al characterization of corners without reference to an underlying classica l spacetime\, and thus might be regarded as the building blocks of a quant um theory.\n LOCATION:https://researchseminars.org/talk/PhysBound/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Laurent Freidel DTSTART:20220316T144000Z DTEND:20220316T152000Z DTSTAMP:20260422T212608Z UID:PhysBound/9 DESCRIPTION:Title: $w_{1+\\infty}$ Higher spin symmetries in gravity and asymptotic charge dynamics\nby Laurent Freidel as part of Physics @ Boundaries Workshop \n\n\nAbstract\nIn this talk\, I will present an analysis\, based on symme tries\, of Einstein's equation in Asymptotically flat spacetime that simpl ifies the asymptotic gravitational dynamics drastically. I will show that the asymptotic Einstein's equation can be recast as conservations equation s for a Carrollian fluid. These conservation equations contain a spin-zero (the mass)\, spin 1 (the momenta) and spin 2 charge aspects. I will show that the spin 2 conservation equation finally gives a symmetry interpretat ion to the subsub-leading soft theorems. It also reveals a higher spin sy mmetry in gravity acting on the gravitational phase space. If time permits \, I will explain the connection with the Celestial CFT derivation of a gl obal version of the symmetry algebra and the challenges that lie ahead.\n LOCATION:https://researchseminars.org/talk/PhysBound/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Malcom Perry DTSTART:20220317T130000Z DTEND:20220317T134000Z DTSTAMP:20260422T212608Z UID:PhysBound/10 DESCRIPTION:Title: Is there a Future in Black Holes?\nby Malcom Perry as part of Physi cs @ Boundaries Workshop\n\n\nAbstract\nI will start with a brief review s ome of the problems associated\nwith the information paradox. I will then move on to a discussion of\ngravitational collapse and the formation of si ngularities in classical\ngeneral relativity. We then look at quantum grav ity and the Wheeler-DeWitt\nequation. We use this to make deductions about the nature of singularities\nquantum mechanically. Finally\, we suggest t hat our results lead to a\npossible route to a resolution of the informati on paradox.\n LOCATION:https://researchseminars.org/talk/PhysBound/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Mahdi Godazgar DTSTART:20220317T135000Z DTEND:20220317T143000Z DTSTAMP:20260422T212608Z UID:PhysBound/11 DESCRIPTION:Title: Dual gravitational charges\nby Mahdi Godazgar as part of Physics @ Boundaries Workshop\n\n\nAbstract\nI will explain how one can derive dual asymptotic gravitational charges using the first-order tetrad formalism. I will then explain why such dual charges are important.\n LOCATION:https://researchseminars.org/talk/PhysBound/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Glenn Barnich DTSTART:20220317T144000Z DTEND:20220317T152000Z DTSTAMP:20260422T212608Z UID:PhysBound/12 DESCRIPTION:Title: A phase transition of photons and gravitons in a Casimir box\nby Gl enn Barnich as part of Physics @ Boundaries Workshop\n\n\nAbstract\nAfter deriving the modular covariant partition function of photons and gravitons with perfectly conducting boundary conditions in a slab geometry\, we inf er consequences for the behavior of these gases at criticality.\n LOCATION:https://researchseminars.org/talk/PhysBound/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Reza Javadinezhad DTSTART:20220318T130000Z DTEND:20220318T134000Z DTSTAMP:20260422T212608Z UID:PhysBound/13 DESCRIPTION:Title: Supertranslation-Invariant Dressed Lorentz Charges\nby Reza Javadin ezhad as part of Physics @ Boundaries Workshop\n\n\nAbstract\nWe present a n explicit formula for Lorentz boosts and rotations that commute with BMS supertranslations in asymptotically flat spacetimes. Key to the constructi on is the use of infrared regularizations and of a unitary transformation that makes observables commute with the soft degrees of freedom. We explic itly verify that our charges satisfy the Lorentz algebra and we check that they are consistent with expectations by evaluating them on the supertran slated Minkowski space and on the boosted Kerr black hole.\n LOCATION:https://researchseminars.org/talk/PhysBound/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Hong Liu DTSTART:20220318T135000Z DTEND:20220318T143000Z DTSTAMP:20260422T212608Z UID:PhysBound/14 DESCRIPTION:Title: Emergent times in holography\nby Hong Liu as part of Physics @ Boun daries Workshop\n\n\nAbstract\nIn holographic duality an eternal AdS black hole is described by two copies of the boundary CFT in the thermal field double state. We provide explicit constructions in the boundary theory of Kruskal-like time evolutions which can take bulk observers behind the hori zon. The constructions also help to illuminate the boundary emergence of t he black hole horizons\, the interiors\, and the associated causal structu re. A key element is the emergence\, in the large N limit of the boundary theory\, of a type III1 von Neumann algebraic structure and the half-sided modular translation structure associated with it.\n LOCATION:https://researchseminars.org/talk/PhysBound/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Edward Witten DTSTART:20220318T144000Z DTEND:20220318T152000Z DTSTAMP:20260422T212608Z UID:PhysBound/15 DESCRIPTION:Title: Why Does The Gravitational Path Integral Appear to Produce Ensemble-Ave raged Answers?\nby Edward Witten as part of Physics @ Boundaries Works hop\n\n\nAbstract\nI will argue that apparent ensemble averaging in gravit y even when there is actually no ensemble reflects two facts: 1) black ho le physics is chaotic\, and 2) the Hamiltonian H_N that describes black ho les has no regular behavior for large N except what follows from thermodyn amics. This interpretation predicts that the gravitational path integral does not show signs of ensemble averaging if one computes the energies an d couplings of states that are not black holes. In D=3\, this prediction can be checked by studying classical solutions\, and passes the test.\n LOCATION:https://researchseminars.org/talk/PhysBound/15/ END:VEVENT END:VCALENDAR