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:20260404T094547Z UID:PhysBound/1 DESCRIPTION:Title: Tails and memories: Monsieur Théophile de Donder meets Sir Herma nn Bondi\nby Geoffrey Compère as part of Physics @ Boundaries Worksho p\n\n\nAbstract\nThe multipolar post-Minkowskian formalism describes the e xternal gravitational field outside sources such as a compact binary merge r. In this formalism\, the metric is expanded in harmonic gauge\, also kno wn as de Donder gauge. In radiation zone\, at length scales above the grav itational wave typical wavelength\, the metric is best studied in Bondi or Newman-Unti gauge where an infinite set of flux-balance laws describe muc h physics of interest. In this talk\, I will describe how to transfer know n results 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 tail and memory effects from this point of view\, as well the descript ion of recently defined $w(1+\\infty)$ charges in terms of canonical multi pole moments.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Laura Donnay DTSTART:20220314T135000Z DTEND:20220314T143000Z DTSTAMP:20260404T094547Z UID:PhysBound/2 DESCRIPTION:Title: A Carrollian Perspective on Celestial Holography\nby Laura Do nnay as part of Physics @ Boundaries Workshop\n\n\nAbstract\nA Carrollian Perspective on Celestial Holography\nAbstract: In this talk\, we will pres ent a holographic description of gravity in 4d asymptotically flat spaceti me in terms of a 3d sourced conformal Carrollian field theory. The externa l sources encode the leaks of gravitational radiation at null infinity. Th e Ward identities of this theory are shown to reproduce those of the 2d ce lestial CFT after relating Carrollian to celestial operators. This suggest s a new set of interplays between gravity in asymptotically flat spacetime \, sourced conformal Carrollian field theory and celestial CFT.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Ted Jacobson(Substituted by Rodrigo Andrade e Silva) DTSTART:20220314T144000Z DTEND:20220314T152000Z DTSTAMP:20260404T094547Z UID:PhysBound/3 DESCRIPTION:Title: Causal diamonds in 2+1 dimensional quantum gravity\nby Ted Ja cobson(Substituted by Rodrigo Andrade e Silva) as part of Physics @ Bounda ries Workshop\n\n\nAbstract\nWe identify the reduced phase space of causal diamonds with fixed edge\nlength in pure 2+1 dimensional gravity with a n egative cosmological constant\,\nwhich turns out to be the cotangent bundl e of the homogeneous space\n$Diff^+(S^1)/PSL(2\,R)$. Isham’s group theor etic quantization scheme is applied to\nthis nonlinear phase space. We fin d that the twist of the boundary curve (which\nis also the ``spin” of th e diamond) is quantized in integer or half-integer\nmultiples of the ratio of the Planck length to the diamond edge length.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Marc Geiller DTSTART:20220315T130000Z DTEND:20220315T134000Z DTSTAMP:20260404T094547Z UID:PhysBound/4 DESCRIPTION:Title: The partial Bondi gauge\nby Marc Geiller as part of Physics @ Boundaries Workshop\n\n\nAbstract\nI will present an analysis of 4d gravi ty in a partial Bondi gauge\, where only three conditions instead of the u sual four are imposed on the metric. The so-called determinant condition u sually imposed on the angular metric is in particular dropped. This partia l gauge still enables to construct a solution space\, which can accommodat e an arbitrary cosmological constant\, boundary sources\, the ''trace of t he shear''\, and polyhomogeneous terms. After presenting this solution spa ce I will discuss the asymptotic symmetries. The partial gauge is in parti cular adapted to treating in a unified manner and contrasting the celebrat ed Bondi-Sachs gauge\, and the Newman-Unti gauge\, which we find to be ine quivalent. This latter does indeed enable to access a new asymptotic symme try. This construction generalizes previous work in 3d gravity\, which I w ill also present as further motivation for the 4d extension.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Vahid Taghiloo DTSTART:20220315T135000Z DTEND:20220315T143000Z DTSTAMP:20260404T094547Z UID:PhysBound/5 DESCRIPTION:Title: Null Surface Thermodynamics\nby Vahid Taghiloo as part of Phy sics @ Boundaries Workshop\n\n\nAbstract\nIn this talk\, I'm going to form ulate the D-dimensional Einstein gravity in presence of a codimension one null boundary. As we will see in addition to the bulk degrees of freedom t hat propagate into the bulk we also have to account for the boundary degre es of freedom that reside at the boundary. A suitable way to label these b oundary degrees of freedom is using the surface charges associated with la rge diffeomorphisms. Surprisingly\, we will also observe these boundary de grees of freedom describe a thermodynamic system with local laws of thermo dynamics. This thermodynamical system is generally an open system and can be closed only when there is no flux of gravitons through the null surface . Local laws of thermodynamics are a manifestation of diffeomorphism invar iance of the theory at the boundary and account for the dynamics of the pa rt of spacetime behind the boundary. Our analysis extends the usual black hole thermodynamics to a universal feature of any area element on a generi c null surface in a generic diffeomorphism invariant theory of gravity.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrew Strominger DTSTART:20220315T144000Z DTEND:20220315T152000Z DTSTAMP:20260404T094547Z UID:PhysBound/6 DESCRIPTION:Title: The Universe as a Quantum Encoder\nby Andrew Strominger as pa rt of Physics @ Boundaries Workshop\n\n\nAbstract\nArguments are given tha t time evolution in an expanding universe is a non-unitary isometry.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Grumiller DTSTART:20220316T130000Z DTEND:20220316T134000Z DTSTAMP:20260404T094547Z UID:PhysBound/7 DESCRIPTION:Title: Near Horizon Symmetries\nby Daniel Grumiller as part of Physi cs @ Boundaries Workshop\n\n\nAbstract\nPhysics at null boundaries is rele vant in flat space holography and for black holes. I focus on the latter\ , reviewing near horizon symmetries and their implications for soft hair\, black hole entropy\, phase space \nslicings\, and memory effects.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Robert Leigh DTSTART:20220316T135000Z DTEND:20220316T143000Z DTSTAMP:20260404T094547Z UID:PhysBound/8 DESCRIPTION:Title: Symmetries of Diff-invariant theories\nby Robert Leigh as par t of Physics @ Boundaries Workshop\n\n\nAbstract\nIn this talk\, I will co nsider a universal group of symmetries that are associated to embedded sur faces in a classical spacetime. In the codimension-2 case\, we refer to th ese surfaces as corners\, and the symmetry as the extended corner symmetry . In the context of the Einstein-Hilbert theory\, we show that the Noether charges supported by such a corner coincide precisely with the extended c orner symmetry. The inclusion of the embedding map into the phase space of the theory allows for a calculation of the algebra of charges. We then sh ow that within the covariant phase space formalism\, there is a precise wa y of extending the phase space such that all charges are integrable and as sociated with Hamiltonian vector fields on field space. The algebra of cha rges is then consistently represented in terms of the Poisson brackets of this extended phase space theory. This resolves an old conundrum in gravit y\, separating the notion of non-integrability from non-conservation. Fina lly\, we discuss some recent work employing the orbit method which relates corners to certain symplectic reductions. This gives an entirely group th eoretical characterization of corners without reference to an underlying c lassical spacetime\, and thus might be regarded as the building blocks of a quantum theory.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Laurent Freidel DTSTART:20220316T144000Z DTEND:20220316T152000Z DTSTAMP:20260404T094547Z 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 W orkshop\n\n\nAbstract\nIn this talk\, I will present an analysis\, based o n symmetries\, of Einstein's equation in Asymptotically flat spacetime tha t simplifies the asymptotic gravitational dynamics drastically. I will sho w that the asymptotic Einstein's equation can be recast as conservations e quations for a Carrollian fluid. These conservation equations contain a sp in-zero (the mass)\, spin 1 (the momenta) and spin 2 charge aspects. I wil l show that the spin 2 conservation equation finally gives a symmetry inte rpretation to the subsub-leading soft theorems. It also reveals a higher spin symmetry in gravity acting on the gravitational phase space. If time permits\, I will explain the connection with the Celestial CFT derivation of a global version of the symmetry algebra and the challenges that lie ah ead.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Malcom Perry DTSTART:20220317T130000Z DTEND:20220317T134000Z DTSTAMP:20260404T094547Z UID:PhysBound/10 DESCRIPTION:Title: Is there a Future in Black Holes?\nby Malcom Perry as part o f Physics @ Boundaries Workshop\n\n\nAbstract\nI will start with a brief r eview some of the problems associated\nwith the information paradox. I wil l then move on to a discussion of\ngravitational collapse and the formatio n of singularities in classical\ngeneral relativity. We then look at quant um gravity and the Wheeler-DeWitt\nequation. We use this to make deduction s about the nature of singularities\nquantum mechanically. Finally\, we su ggest that our results lead to a\npossible route to a resolution of the in formation paradox.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Mahdi Godazgar DTSTART:20220317T135000Z DTEND:20220317T143000Z DTSTAMP:20260404T094547Z UID:PhysBound/11 DESCRIPTION:Title: Dual gravitational charges\nby Mahdi Godazgar as part of Phy sics @ Boundaries Workshop\n\n\nAbstract\nI will explain how one can deriv e dual asymptotic gravitational charges using the first-order tetrad forma lism. I will then explain why such dual charges are important.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Glenn Barnich DTSTART:20220317T144000Z DTEND:20220317T152000Z DTSTAMP:20260404T094547Z UID:PhysBound/12 DESCRIPTION:Title: A phase transition of photons and gravitons in a Casimir box \nby Glenn Barnich as part of Physics @ Boundaries Workshop\n\n\nAbstract\ nAfter deriving the modular covariant partition function of photons and gr avitons with perfectly conducting boundary conditions in a slab geometry\, we infer consequences for the behavior of these gases at criticality.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Reza Javadinezhad DTSTART:20220318T130000Z DTEND:20220318T134000Z DTSTAMP:20260404T094547Z UID:PhysBound/13 DESCRIPTION:Title: Supertranslation-Invariant Dressed Lorentz Charges\nby Reza Javadinezhad as part of Physics @ Boundaries Workshop\n\n\nAbstract\nWe pr esent an explicit formula for Lorentz boosts and rotations that commute wi th BMS supertranslations in asymptotically flat spacetimes. Key to the con struction is the use of infrared regularizations and of a unitary transfor mation that makes observables commute with the soft degrees of freedom. We explicitly verify that our charges satisfy the Lorentz algebra and we che ck that they are consistent with expectations by evaluating them on the su pertranslated Minkowski space and on the boosted Kerr black hole.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Hong Liu DTSTART:20220318T135000Z DTEND:20220318T143000Z DTSTAMP:20260404T094547Z UID:PhysBound/14 DESCRIPTION:Title: Emergent times in holography\nby Hong Liu as part of Physics @ Boundaries Workshop\n\n\nAbstract\nIn holographic duality an eternal Ad S black hole is described by two copies of the boundary CFT in the thermal field double state. We provide explicit constructions in the boundary the ory of Kruskal-like time evolutions which can take bulk observers behind t he horizon. The constructions also help to illuminate the boundary emergen ce of the black hole horizons\, the interiors\, and the associated causal structure. A key element is the emergence\, in the large N limit of the bo undary theory\, of a type III1 von Neumann algebraic structure and the hal f-sided modular translation structure associated with it.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Edward Witten DTSTART:20220318T144000Z DTEND:20220318T152000Z DTSTAMP:20260404T094547Z UID:PhysBound/15 DESCRIPTION:Title: Why Does The Gravitational Path Integral Appear to Produce Ensem ble-Averaged Answers?\nby Edward Witten as part of Physics @ Boundarie s Workshop\n\n\nAbstract\nI will argue that apparent ensemble averaging in gravity even when there is actually no ensemble reflects two facts: 1) b lack hole physics is chaotic\, and 2) the Hamiltonian H_N that describes b lack holes has no regular behavior for large N except what follows from th ermodynamics. This interpretation predicts that the gravitational path i ntegral does not show signs of ensemble averaging if one computes the ener gies and couplings of states that are not black holes. In D=3\, this pre diction can be checked by studying classical solutions\, and passes the te st.\n LOCATION:https://stable.researchseminars.org/talk/PhysBound/15/ END:VEVENT END:VCALENDAR