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BEGIN:VEVENT
SUMMARY:Alex Maloney (McGill University)
DTSTART:20200623T193000Z
DTEND:20200623T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/2
DESCRIPTION:Title: Gravity from Averaging CFTs\nby Alex Maloney (McGill Univers
ity) as part of UBC String Theory Seminars\n\n\nAbstract\nI will explore t
he idea that certain theories of gravity in Anti-de Sitter space are dual
to an average over an ensemble of quantum theories\, rather than to a spec
ific quantum theory. I will describe an average over Narain’s family of
two-dimensional conformal field theories which describe free bosons on a
torus\, and compute the partition function using the Siegel-Weil formula.
The result takes the form of a sum over geometries as one would expect in
a theory of gravity. But the gravitational theory looks more like a Che
rn-Simons theory than like Einstein gravity.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Netta Engelhardt (MIT)
DTSTART:20200817T193000Z
DTEND:20200817T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/3
DESCRIPTION:Title: Free Energy from Replica Wormholes\nby Netta Engelhardt (MIT
) as part of UBC String Theory Seminars\n\n\nAbstract\nRecent developments
on the black hole information paradox have shown that Euclidean wormholes
— so called “replica wormholes’’ can dominate the von Neumann ent
ropy as computed by a gravitational path integral\, and that inclusion of
these wormholes results in a unitary Page curve. This development raises s
ome puzzles from the perspective of factorization\, and has raised questio
ns regarding what the gravitational path integral is computing. In this ta
lk\, I will focus on understanding the relationship between the gravitatio
nal path integral and the partition function via the gravitational free en
ergy (more generally the generating functional). A proper computation of t
he free energy requires a replica trick distinct from the usual one used t
o compute the entropy. I will show that in JT gravity there is a regime wh
ere the free energy computed without replica wormholes is pathological. In
terestingly\, the inclusion of replica wormholes is not quite sufficient t
o resolve the pathology: an alternative analytic continuation is required.
I will discuss the implications of this for various interpretations of th
e gravitational path integral (e.g. as computing an ensemble average) and
also mention some parallels with spin glasses.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tom Hartman (Cornell)
DTSTART:20200914T193000Z
DTEND:20200914T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/4
DESCRIPTION:Title: Islands in cosmology\nby Tom Hartman (Cornell) as part of UB
C String Theory Seminars\n\n\nAbstract\nA quantum extremal island suggests
that a region of spacetime is encoded in the quantum state of another sys
tem\, like the encoding of the black hole interior in Hawking radiation. I
will discuss the relationship between islands and the Bekenstein bound\,
other information-theoretic constraints\, and applications to four-dimensi
onal FRW cosmology.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chris Akers (MIT)
DTSTART:20200928T193000Z
DTEND:20200928T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/5
DESCRIPTION:Title: Leading order corrections to the quantum extremal surface prescr
iption\nby Chris Akers (MIT) as part of UBC String Theory Seminars\n\n
\nAbstract\nThe QES prescription is the holographic method for computing v
on Neumann entropy\, telling us in particular how quantum effects in the b
ulk affect the entropy of the dual CFT. That these quantum effects can be
significant underlies the impactful updates to the information loss puzzle
from last year.\n\nI will explain a further development that comes from s
tudying significant quantum effects: a naive application of the QES prescr
iption can lead to contradictory results and must be corrected\, at leadin
g order\, in certain situations. I will explain the source of these correc
tions\, exactly when they occur\, and what they mean for all results predi
cated on the QES prescription.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Horacio Casini
DTSTART:20201005T193000Z
DTEND:20201005T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/6
DESCRIPTION:Title: Entropic order parameters for symmetries in QFT\nby Horacio
Casini as part of UBC String Theory Seminars\n\n\nAbstract\nIn QFT there i
s an algebra of operators attached to any spacetime region. Simple degrada
tions of the most harmonious possible relation between algebras and region
s are shown to encode generalized symmetries. Nets of algebras with these
symmetries allow for a non uniqueness of the algebras that can be assigned
to a given region. This non uniqueness suggests a simple geometrical orde
r parameter in terms of a relative entropy. These satisfy a ''certainty re
lation'' connecting the statistics of the order and disorder parameters fo
r complementary regions. We describe how the usual lore about phases of th
eories with generalized symmetries is recovered in this new picture.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Clifford Johnson (USC)
DTSTART:20201019T190000Z
DTEND:20201019T203000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/7
DESCRIPTION:Title: Non-perturbative physics for JT gravity and supergravity\nb
y Clifford Johnson (USC) as part of UBC String Theory Seminars\n\n\nAbstra
ct\nJackiw–Teitelboim (JT) gravity and supergravity theories are excitin
g solvable models that teach us about low temperature black hole dynamics\
, and aspects of quantum chaotic behaviour. They have been shown (by Saad\
, Shenker and Stanford\, and by Stanford and Witten) to have double scaled
random matrix model descriptions\, capturing the (spacetime) topological
perturbative expansion of the partition function. I will describe an alte
rnative method for building the matrix model description\, using technique
s from minimal string theory. This method is particularly useful for suppl
ying non-perturbative definitions of the physics. I show how this allows f
or the computation of key aspects of the physics at low energy and tempera
ture.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Antony Speranza
DTSTART:20201102T203000Z
DTEND:20201102T220000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/8
DESCRIPTION:Title: Anomalies in gravitational charge algebras of null boundaries an
d black hole entropy\nby Antony Speranza as part of UBC String Theory
Seminars\n\n\nAbstract\nI will discuss how the central charges appearing i
n near-horizon symmetry algebras arise from an anomalous transformation of
the null boundary term in the gravitational action. This parallels the w
ay in which the holographic Weyl anomaly appears in AdS/CFT\, with the amb
iguity in the normalization of the null generator being the analogue of th
e choice of Weyl frame. As an application\, I will analyze a generalizati
on of the near-horizon Virasoro symmetries of Haco\, Hawking\, Perry\, and
Strominger\, and give a systematic derivation of the Wald-Zoupas fluxes a
nd central charges. In particular\, I will discuss a way to define the qu
asilocal charges unambiguously\, and show that the central charge computed
by the charge algebra is directly related to the horizon entropy via the
Cardy formula. \nBased on https://arxiv.org/abs/2009.10739 and\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jim Halverson (Northeastern)
DTSTART:20201109T203000Z
DTEND:20201109T220000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/9
DESCRIPTION:Title: Neural Networks and Quantum Field Theory\nby Jim Halverson (
Northeastern) as part of UBC String Theory Seminars\n\n\nAbstract\nWe prop
ose a theoretical understanding of neural networks in terms of Wilsonian e
ffective field theory. The correspondence relies on the fact that many asy
mptotic neural networks are drawn from Gaussian processes\, the analog of
non-interacting field theories. Moving away from the asymptotic limit yiel
ds a non-Gaussian process and corresponds to turning on particle interacti
ons\, allowing for the computation of correlation functions of neural netw
ork outputs with Feynman diagrams. Minimal non-Gaussian process likelihood
s are determined by the most relevant non-Gaussian terms\, according to th
e flow in their coefficients induced by the Wilsonian renormalization grou
p. This yields a direct connection between overparameterization and simpli
city of neural network likelihoods. Whether the coefficients are constants
or functions may be understood in terms of GP limit symmetries\, as expec
ted from 't Hooft's technical naturalness. General theoretical calculation
s are matched to neural network experiments in the simplest class of model
s allowing the correspondence. Our formalism is valid for any of the many
architectures that becomes a GP in an asymptotic limit\, a property preser
ved under certain types of training.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Lorenz Eberhardt (IAS)
DTSTART:20210510T193000Z
DTEND:20210510T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/10
DESCRIPTION:Title: Summing over geometries in string theory\nby Lorenz Eberhar
dt (IAS) as part of UBC String Theory Seminars\n\n\nAbstract\nI discuss th
e question how string theory achieves a sum over bulk geometries with fixe
d asymptotic boundary conditions. I analyze this problem with the help of
the tensionless string on AdS3xS3xT4 (with one unit of NS-NS flux) that wa
s recently understood to be dual to the symmetric orbifold of T4. I argue
that large stringy corrections around a fixed background can be interprete
d as different semiclassical geometries\, thus making a sum over semi-clas
sical geometries superfluous.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matthias Gaberdiel (ETH Zurich)
DTSTART:20210517T170000Z
DTEND:20210517T183000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/11
DESCRIPTION:Title: The String Dual of Free N=4 SYM\nby Matthias Gaberdiel (ETH
Zurich) as part of UBC String Theory Seminars\n\n\nAbstract\nWe propose a
world-sheet description for string theory on AdS5 x S5 that reproduces ex
actly the planar spectrum of free N=4 SYM in 4d. Our ansatz is inspired by
the world-sheet description for tensionless strings on AdS3 x S3 x T4 tha
t was previously shown to reproduce precisely the symmetric orbifold of T4
. (Based on joint work with Rajesh Gopakumar.)\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xiao-Liang Qi (Stanford)
DTSTART:20210614T193000Z
DTEND:20210614T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/12
DESCRIPTION:Title: Entanglement island\, miracle operators and the firewall\nb
y Xiao-Liang Qi (Stanford) as part of UBC String Theory Seminars\n\n\nAbst
ract\nIn this paper\, we obtain some general results on information retrie
val from the black hole interior\, based on the recent progress on quantum
extremal surface formula and entanglement island. We study an AdS black h
ole coupled to a bath with generic dynamics\, and ask whether it is possib
le to retrieve information about a small perturbation in the interior from
the bath system. We derive a state reconstruction formula based on one no
rm. However\, we show that a contradiction arises if we apply this result
to a special situation when the bath dynamics includes a unitary operation
that carries a particular measurement to a region A and send the result t
o another region W. Physically\, the contradiction arises between transfer
ability of classical information during the measurement\, and non-transfer
ability of quantum information which determines the entanglement island. W
e propose that the resolution of the contradiction is to realize that the
state reconstruction formula does not apply to the special situation invol
ving interior-information-retrieving measurements. This implies that the a
ssumption of smooth replica AdS geometry with boundary condition set by th
e flat space bath has to break down when the particular measurement operat
or is applied to the bath. Using replica trick\, we introduce an explicitl
y construction of such operator\, which we name as "miracle operators". Fr
om this construction we see that the smooth replica geometry assumption br
eaks down because we have to introduce extra replica wormholes connecting
with the "simulated blackholes" introduced by the miracle operator. We stu
dy the implication of miracle operators in understanding the firewall para
dox.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:David Kolchmeyer (Harvard)
DTSTART:20210531T193000Z
DTEND:20210531T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/13
DESCRIPTION:Title: Dynamical End-of-the-World Branes in Jackiw-Teitelboim Gravity<
/a>\nby David Kolchmeyer (Harvard) as part of UBC String Theory Seminars\n
\n\nAbstract\nJackiw-Teitelboim gravity with end-of-the-world (EoW) branes
has been used to study the black hole information problem. In this talk\,
I consider dynamical EoW branes by summing over loops of branes in the Eu
clidean path integral. The UV divergences that arise are treated in the co
ntext of effective field theory. The effective field theory perspective ha
s a natural interpretation in the dual matrix model. The EoW branes make a
contribution to the black hole entropy that is consistent with a state-co
unting interpretation of the entropy. This mechanism resolves a version of
the information problem that has been formulated in this model. I will al
so discuss a related problem that is not resolved by dynamical EoW branes.
\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:David Kolchmeyer
DTSTART:20210531T193000Z
DTEND:20210531T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/14
DESCRIPTION:by David Kolchmeyer as part of UBC String Theory Seminars\n\nA
bstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pranjal Nayak
DTSTART:20210621T193000Z
DTEND:20210621T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/15
DESCRIPTION:Title: From operator statistics to wormholes\nby Pranjal Nayak as
part of UBC String Theory Seminars\n\n\nAbstract\nFor a generic quantum ma
ny-body system\, the quantum ergodic regime is defined as the limit in whi
ch the spectrum of the system resembles that of a random matrix theory (RM
T) in the corresponding symmetry class. In this talk I will discuss the ti
me dependence of correlation functions of operators in the SYK model\, in
the ergodic limit as well as their approach to the ergodic limit which is
controlled by non-universal massive modes. An effective field theory (EFT)
corresponding to the causal symmetry and its breaking describes the ergod
ic phase. I will discuss the topological expansion of the resulting Goldst
one-mode theory where the leading non-trivial topologies give rise to the
universal ramp seen in correlation functions. Furthermore we analytically
capture the plateau behaviour by taking into account the contribution of a
second saddle point. These results explicitly establish the validity of t
he EFT description in the SYK-class of models\, starting from their micros
copic description. I will discuss the tower of massive modes above the Gol
dstone sector that govern how the ergodic EFT phase is approached and deri
ve the relevant Thouless time scales.\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Josephine Suh
DTSTART:20211014T193000Z
DTEND:20211014T210000Z
DTSTAMP:20260404T094428Z
UID:UBCStrings/16
DESCRIPTION:Title: Quantum gravity from probability\nby Josephine Suh as part
of UBC String Theory Seminars\n\n\nAbstract\nWe propose that the underlyin
g context of the Ryu-Takayanagi formula and of holographic duality is that
the volume measure of spacetime is a probability measure constrained by q
uantum dynamics. In anti-de Sitter Jackiw-Teitelboim gravity\, we define a
nd analyze a quantum stochastic process induced by the boundary. Taking th
e asymptotic limit of the process at short time scales and flat space\, we
find that Einstein’s equations of the bulk theory\, sans the cosmologic
al constant term\, arise in the semi-classical limit of the quantum evolut
ion of probability under the process. Extrapolating from these and analogo
us results in the full theory of AdS JT gravity\, we conjecture that gener
al relativity arises in the semi-classical limit of the evolution of proba
bility with respect to quantum stochastic processes.\n\n(Based on https://
arxiv.org/abs/2108.10916 and work in preparation.)\n\nJoin Zoom Meeting: h
ttps://ubc.zoom.us/j/68265308064?pwd=Y2FTOGdWSCszYlNQVWhxR1BKbW81QT09\n\nM
eeting ID: 682 6530 8064\n\nPasscode: 104685\n
LOCATION:https://stable.researchseminars.org/talk/UBCStrings/16/
END:VEVENT
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