BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Alex Maloney (McGill University) DTSTART:20200623T193000Z DTEND:20200623T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/2 DESCRIPTION:Title: Gravity from Averaging CFTs\nby Alex Maloney (McGill University) as part of UBC String Theory Seminars\n\n\nAbstract\nI will explore the idea that certain theories of gravity in Anti-de Sitter space are dual to an a verage over an ensemble of quantum theories\, rather than to a specific qu antum theory. I will describe an average over Narain’s family of two-di mensional conformal field theories which describe free bosons on a torus\, and compute the partition function using the Siegel-Weil formula. The re sult takes the form of a sum over geometries as one would expect in a theo ry of gravity. But the gravitational theory looks more like a Chern-Simo ns theory than like Einstein gravity.\n LOCATION:https://researchseminars.org/talk/UBCStrings/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Netta Engelhardt (MIT) DTSTART:20200817T193000Z DTEND:20200817T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/3 DESCRIPTION:Title: Free Energy from Replica Wormholes\nby Netta Engelhardt (MIT) as pa rt 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 entropy as computed by a gravitational path integral\, and that inclusion of these w ormholes results in a unitary Page curve. This development raises some puz zles from the perspective of factorization\, and has raised questions rega rding what the gravitational path integral is computing. In this talk\, I will focus on understanding the relationship between the gravitational pat h integral and the partition function via the gravitational free energy (m ore generally the generating functional). A proper computation of the free energy requires a replica trick distinct from the usual one used to compu te the entropy. I will show that in JT gravity there is a regime where the free energy computed without replica wormholes is pathological. Interesti ngly\, the inclusion of replica wormholes is not quite sufficient to resol ve the pathology: an alternative analytic continuation is required. I will discuss the implications of this for various interpretations of the gravi tational path integral (e.g. as computing an ensemble average) and also me ntion some parallels with spin glasses.\n LOCATION:https://researchseminars.org/talk/UBCStrings/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Tom Hartman (Cornell) DTSTART:20200914T193000Z DTEND:20200914T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/4 DESCRIPTION:Title: Islands in cosmology\nby Tom Hartman (Cornell) as part of UBC Strin g Theory Seminars\n\n\nAbstract\nA quantum extremal island suggests that a region of spacetime is encoded in the quantum state of another system\, l ike the encoding of the black hole interior in Hawking radiation. I will d iscuss the relationship between islands and the Bekenstein bound\, other i nformation-theoretic constraints\, and applications to four-dimensional FR W cosmology.\n LOCATION:https://researchseminars.org/talk/UBCStrings/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Chris Akers (MIT) DTSTART:20200928T193000Z DTEND:20200928T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/5 DESCRIPTION:Title: Leading order corrections to the quantum extremal surface prescription< /a>\nby Chris Akers (MIT) as part of UBC String Theory Seminars\n\n\nAbstr act\nThe QES prescription is the holographic method for computing von Neum ann entropy\, telling us in particular how quantum effects in the bulk aff ect the entropy of the dual CFT. That these quantum effects can be signifi cant underlies the impactful updates to the information loss puzzle from l ast year.\n\nI will explain a further development that comes from studying significant quantum effects: a naive application of the QES prescription can lead to contradictory results and must be corrected\, at leading order \, in certain situations. I will explain the source of these corrections\, exactly when they occur\, and what they mean for all results predicated o n the QES prescription.\n LOCATION:https://researchseminars.org/talk/UBCStrings/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Horacio Casini DTSTART:20201005T193000Z DTEND:20201005T210000Z DTSTAMP:20260422T225819Z 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 is an al gebra of operators attached to any spacetime region. Simple degradations o f the most harmonious possible relation between algebras and regions are s hown to encode generalized symmetries. Nets of algebras with these symmetr ies allow for a non uniqueness of the algebras that can be assigned to a g iven region. This non uniqueness suggests a simple geometrical order param eter in terms of a relative entropy. These satisfy a ''certainty relation' ' connecting the statistics of the order and disorder parameters for compl ementary regions. We describe how the usual lore about phases of theories with generalized symmetries is recovered in this new picture.\n LOCATION:https://researchseminars.org/talk/UBCStrings/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Clifford Johnson (USC) DTSTART:20201019T190000Z DTEND:20201019T203000Z DTSTAMP:20260422T225819Z UID:UBCStrings/7 DESCRIPTION:Title: Non-perturbative physics for JT gravity and supergravity\nby Cliff ord Johnson (USC) as part of UBC String Theory Seminars\n\n\nAbstract\nJac kiw–Teitelboim (JT) gravity and supergravity theories are exciting solva ble models that teach us about low temperature black hole dynamics\, and a spects of quantum chaotic behaviour. They have been shown (by Saad\, Shenk er and Stanford\, and by Stanford and Witten) to have double scaled random matrix model descriptions\, capturing the (spacetime) topological pertur bative expansion of the partition function. I will describe an alternative method for building the matrix model description\, using techniques from minimal string theory. This method is particularly useful for supplying no n-perturbative definitions of the physics. I show how this allows for the computation of key aspects of the physics at low energy and temperature.\n LOCATION:https://researchseminars.org/talk/UBCStrings/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Antony Speranza DTSTART:20201102T203000Z DTEND:20201102T220000Z DTSTAMP:20260422T225819Z UID:UBCStrings/8 DESCRIPTION:Title: Anomalies in gravitational charge algebras of null boundaries and black hole entropy\nby Antony Speranza as part of UBC String Theory Seminar s\n\n\nAbstract\nI will discuss how the central charges appearing in near- horizon symmetry algebras arise from an anomalous transformation of the nu ll boundary term in the gravitational action. This parallels the way in w hich the holographic Weyl anomaly appears in AdS/CFT\, with the ambiguity in the normalization of the null generator being the analogue of the choic e of Weyl frame. As an application\, I will analyze a generalization of t he near-horizon Virasoro symmetries of Haco\, Hawking\, Perry\, and Stromi nger\, and give a systematic derivation of the Wald-Zoupas fluxes and cent ral charges. In particular\, I will discuss a way to define the quasiloca l charges unambiguously\, and show that the central charge computed by the charge algebra is directly related to the horizon entropy via the Cardy f ormula. \nBased on https://arxiv.org/abs/2009.10739 and\n LOCATION:https://researchseminars.org/talk/UBCStrings/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Jim Halverson (Northeastern) DTSTART:20201109T203000Z DTEND:20201109T220000Z DTSTAMP:20260422T225819Z UID:UBCStrings/9 DESCRIPTION:Title: Neural Networks and Quantum Field Theory\nby Jim Halverson (Northea stern) as part of UBC String Theory Seminars\n\n\nAbstract\nWe propose a t heoretical understanding of neural networks in terms of Wilsonian effectiv e field theory. The correspondence relies on the fact that many asymptotic neural networks are drawn from Gaussian processes\, the analog of non-int eracting field theories. Moving away from the asymptotic limit yields a no n-Gaussian process and corresponds to turning on particle interactions\, a llowing for the computation of correlation functions of neural network out puts with Feynman diagrams. Minimal non-Gaussian process likelihoods are d etermined by the most relevant non-Gaussian terms\, according to the flow in their coefficients induced by the Wilsonian renormalization group. This yields a direct connection between overparameterization and simplicity of neural network likelihoods. Whether the coefficients are constants or fun ctions may be understood in terms of GP limit symmetries\, as expected fro m 't Hooft's technical naturalness. General theoretical calculations are m atched to neural network experiments in the simplest class of models allow ing the correspondence. Our formalism is valid for any of the many archite ctures that becomes a GP in an asymptotic limit\, a property preserved und er certain types of training.\n LOCATION:https://researchseminars.org/talk/UBCStrings/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Lorenz Eberhardt (IAS) DTSTART:20210510T193000Z DTEND:20210510T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/10 DESCRIPTION:Title: Summing over geometries in string theory\nby Lorenz Eberhardt (IAS ) as part of UBC String Theory Seminars\n\n\nAbstract\nI discuss the quest ion how string theory achieves a sum over bulk geometries with fixed asymp totic boundary conditions. I analyze this problem with the help of the ten sionless string on AdS3xS3xT4 (with one unit of NS-NS flux) that was recen tly understood to be dual to the symmetric orbifold of T4. I argue that la rge stringy corrections around a fixed background can be interpreted as di fferent semiclassical geometries\, thus making a sum over semi-classical g eometries superfluous.\n LOCATION:https://researchseminars.org/talk/UBCStrings/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Matthias Gaberdiel (ETH Zurich) DTSTART:20210517T170000Z DTEND:20210517T183000Z DTSTAMP:20260422T225819Z 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 exactly t he planar spectrum of free N=4 SYM in 4d. Our ansatz is inspired by the wo rld-sheet description for tensionless strings on AdS3 x S3 x T4 that was p reviously shown to reproduce precisely the symmetric orbifold of T4. (Base d on joint work with Rajesh Gopakumar.)\n LOCATION:https://researchseminars.org/talk/UBCStrings/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Xiao-Liang Qi (Stanford) DTSTART:20210614T193000Z DTEND:20210614T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/12 DESCRIPTION:Title: Entanglement island\, miracle operators and the firewall\nby Xiao- Liang Qi (Stanford) as part of UBC String Theory Seminars\n\n\nAbstract\nI n this paper\, we obtain some general results on information retrieval fro m the black hole interior\, based on the recent progress on quantum extrem al surface formula and entanglement island. We study an AdS black hole cou pled to a bath with generic dynamics\, and ask whether it is possible to r etrieve information about a small perturbation in the interior from the ba th system. We derive a state reconstruction formula based on one norm. How ever\, we show that a contradiction arises if we apply this result to a sp ecial situation when the bath dynamics includes a unitary operation that c arries a particular measurement to a region A and send the result to anoth er region W. Physically\, the contradiction arises between transferability of classical information during the measurement\, and non-transferability of quantum information which determines the entanglement island. We propo se that the resolution of the contradiction is to realize that the state r econstruction formula does not apply to the special situation involving in terior-information-retrieving measurements. This implies that the assumpti on of smooth replica AdS geometry with boundary condition set by the flat space bath has to break down when the particular measurement operator is a pplied to the bath. Using replica trick\, we introduce an explicitly const ruction of such operator\, which we name as "miracle operators". From this construction we see that the smooth replica geometry assumption breaks do wn because we have to introduce extra replica wormholes connecting with th e "simulated blackholes" introduced by the miracle operator. We study the implication of miracle operators in understanding the firewall paradox.\n LOCATION:https://researchseminars.org/talk/UBCStrings/12/ END:VEVENT BEGIN:VEVENT SUMMARY:David Kolchmeyer (Harvard) DTSTART:20210531T193000Z DTEND:20210531T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/13 DESCRIPTION:Title: Dynamical End-of-the-World Branes in Jackiw-Teitelboim Gravity\nby David Kolchmeyer (Harvard) as part of UBC String Theory Seminars\n\n\nAbs tract\nJackiw-Teitelboim gravity with end-of-the-world (EoW) branes has be en used to study the black hole information problem. In this talk\, I cons ider dynamical EoW branes by summing over loops of branes in the Euclidean path integral. The UV divergences that arise are treated in the context o f effective field theory. The effective field theory perspective has a nat ural interpretation in the dual matrix model. The EoW branes make a contri bution to the black hole entropy that is consistent with a state-counting interpretation of the entropy. This mechanism resolves a version of the in formation problem that has been formulated in this model. I will also disc uss a related problem that is not resolved by dynamical EoW branes.\n LOCATION:https://researchseminars.org/talk/UBCStrings/13/ END:VEVENT BEGIN:VEVENT SUMMARY:David Kolchmeyer DTSTART:20210531T193000Z DTEND:20210531T210000Z DTSTAMP:20260422T225819Z UID:UBCStrings/14 DESCRIPTION:by David Kolchmeyer as part of UBC String Theory Seminars\n\nA bstract: TBA\n LOCATION:https://researchseminars.org/talk/UBCStrings/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Pranjal Nayak DTSTART:20210621T193000Z DTEND:20210621T210000Z DTSTAMP:20260422T225819Z 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 many-body system\, the quantum ergodic regime is defined as the limit in which the spectrum of the system resembles that of a random matrix theory (RMT) in t he corresponding symmetry class. In this talk I will discuss the time depe ndence of correlation functions of operators in the SYK model\, in the erg odic limit as well as their approach to the ergodic limit which is control led by non-universal massive modes. An effective field theory (EFT) corres ponding to the causal symmetry and its breaking describes the ergodic phas e. I will discuss the topological expansion of the resulting Goldstone-mod e theory where the leading non-trivial topologies give rise to the univers al 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 the EFT description in the SYK-class of models\, starting from their microscopic d escription. I will discuss the tower of massive modes above the Goldstone sector that govern how the ergodic EFT phase is approached and derive the relevant Thouless time scales.\n LOCATION:https://researchseminars.org/talk/UBCStrings/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Josephine Suh DTSTART:20211014T193000Z DTEND:20211014T210000Z DTSTAMP:20260422T225819Z 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 underlying conte xt of the Ryu-Takayanagi formula and of holographic duality is that the vo lume measure of spacetime is a probability measure constrained by quantum dynamics. In anti-de Sitter Jackiw-Teitelboim gravity\, we define and anal yze a quantum stochastic process induced by the boundary. Taking the asymp totic limit of the process at short time scales and flat space\, we find t hat Einstein’s equations of the bulk theory\, sans the cosmological cons tant term\, arise in the semi-classical limit of the quantum evolution of probability under the process. Extrapolating from these and analogous resu lts in the full theory of AdS JT gravity\, we conjecture that general rela tivity arises in the semi-classical limit of the evolution of probability with respect to quantum stochastic processes.\n\n(Based on https://arxiv.o rg/abs/2108.10916 and work in preparation.)\n\nJoin Zoom Meeting: https:// ubc.zoom.us/j/68265308064?pwd=Y2FTOGdWSCszYlNQVWhxR1BKbW81QT09\n\nMeeting ID: 682 6530 8064\n\nPasscode: 104685\n LOCATION:https://researchseminars.org/talk/UBCStrings/16/ END:VEVENT END:VCALENDAR