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BEGIN:VEVENT
SUMMARY:Geoffrey Compère
DTSTART;VALUE=DATE-TIME:20220314T130000Z
DTEND;VALUE=DATE-TIME:20220314T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220314T135000Z
DTEND;VALUE=DATE-TIME:20220314T143000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220314T144000Z
DTEND;VALUE=DATE-TIME:20220314T152000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220315T130000Z
DTEND;VALUE=DATE-TIME:20220315T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220315T135000Z
DTEND;VALUE=DATE-TIME:20220315T143000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220315T144000Z
DTEND;VALUE=DATE-TIME:20220315T152000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220316T130000Z
DTEND;VALUE=DATE-TIME:20220316T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220316T135000Z
DTEND;VALUE=DATE-TIME:20220316T143000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220316T144000Z
DTEND;VALUE=DATE-TIME:20220316T152000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220317T130000Z
DTEND;VALUE=DATE-TIME:20220317T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220317T135000Z
DTEND;VALUE=DATE-TIME:20220317T143000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220317T144000Z
DTEND;VALUE=DATE-TIME:20220317T152000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220318T130000Z
DTEND;VALUE=DATE-TIME:20220318T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220318T135000Z
DTEND;VALUE=DATE-TIME:20220318T143000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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;VALUE=DATE-TIME:20220318T144000Z
DTEND;VALUE=DATE-TIME:20220318T152000Z
DTSTAMP;VALUE=DATE-TIME:20240329T124154Z
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/
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