# String/Gravity Theory Seminar Fall 2021

Organizers: Chris Akers, Netta Engelhardt, Harold Erbin, Ping Gao, Patrick Jefferson, Washington Taylor**Held every** **Wednesday**, 3-4pm EST.

#### Seminars

September 8**Jordan Cotler**, Harvard

Title: Black hole microstate statistics from Euclidean wormholes

September 15**Geoff Penington**, Berkeley

Title: Pythons and Tensor Networks are a Few of My Favorite Things

Abstract: I’ll solve quantum gravity with pythons and/or tensor networks.

September 22

**Daniel** **Mayerson**, IPhT, Saclay

Title: Fuzzball Shadows: Emergent Horizons from Microstructure

Abstract: The advent of black hole imaging has opened a new window into probing the horizon scale of black holes. An important question is whether string theory results for black hole physics can predict interesting and observable features that current and future experiments can probe. I will discuss the physical properties of four-dimensional, string-theoretical, horizonless “fuzzball” geometries by means of imaging their shadows. Their microstructure traps light rays straying near the would-be horizon on long-lived, highly redshifted chaotic orbits. In fuzzballs sufficiently near the scaling limit this creates a shadow much like that of a black hole, while avoiding the paradoxes associated with an event horizon. Finally, I will consider comparing such fuzzball images to their black hole counterparts. In particular, detailed measurements of higher order photon rings have the potential to discriminate between fuzzballs and black holes in future observations.

September 29**Ted Erler, **CEICO (remote)

Title: Relating covariant and lightcone string field theories

Abstract: We describe recent work which aims to construct a field transformation which relates Witten’s open bosonic string field theory and the lightcone string field theory of Kaku and Kikkawa.

October 6**Ashoke Sen**, Harish-Chandra Institute (remote)

Title: D-instanton amplitudes in string theory

Abstract: I shall review the problems in computing D-instanton

contribution to string amplitudes using the usual world-sheet methods, and

recent progress in overcoming these difficulties using insights from

string field theory.

Tuesday, October 12**Jennifer Lin**, Oxford (remote)

Title: A new look at the gravitational entropy formula

Abstract: The Ryu-Takayanagi formula and its generalizations have led to a surprising amount of progress in our understanding of quantum gravity in the last fifteen years, culminating in the recent derivation of the Page curve in toy models of evaporating black holes. However, we still don’t understand why* *these formulas are true from a canonical point of view. In this talk, I will attempt to make progress on this problem by developing an analogy between gravitational entropy formulas in low-dimensional examples of holography and similar-looking formulas that have appeared in the study of entanglement entropy in emergent gauge theories. This talk will be based on 1807.06575, 2107.11872, and 2107.12634.

October 20**Daniel Jafferis**, Harvard

Title: TBA

October 27**Ben Heidenreich**, Amherst (remote)

Title: TBA

November 3**Fabian Ruehle**, Northeastern University

Title: A Physics and a Math Conjecture

Abstract: Recently, many conjectures about the nature of phenomena that can or cannot arise in String Theory or Quantum Gravity have been put forward. One of them, the Swampland Distance Conjecture, relates geodesic motion in the moduli space of compactifications to a change in the spectrum of the theory. Motivated by this, we study geodesics in the Kähler or vector moduli space of Calabi-Yau threefolds described as hypersurfaces or complete intersections in projective or toric ambient spaces. We discuss how geometric flop transitions in these spaces can lead to isomorphic or non-isomorphic Calabi-Yau manifolds. We find that there exist infinite flop chains of isomorphic geometries, but only a finite number of flops to inequivalent manifolds. The latter is expected based on the swampland distance conjecture, and mathematically fits to a conjecture due to Kawamata and Morrison. We also present a classification and analytic solution of all geodesics in 2D (vector) moduli spaces of Calabi-Yau threefolds. The talk is based on 2104.03325 and 2108.10323.

November 9 (Note–this is a Tuesday seminar at 12:15)**Herman Verlinde**, Princeton

Title: Chaos in Celestial CFT

Abstract: Celestial holography proposes that scattering in flat spacetime is captured by a CFT living on the celestial sphere. I argue that the Hilbert space of celestial CFT can be identified with the Hilbert space of an accelerating Rindler observer in the bulk. Rindler particles exhibit Lyapunov behavior when shockwaves shift the observer horizon. I show how this chaotic behavior is encoded in celestial CFT, giving evidence that it describes a maximally chaotic system. I comment on how particles can cross the Rindler horizon via a GWJ quantum teleportation protocol.

November 17**Brian Swingle, **Brandeis

Title: Effective Field Theory of Chaotic Spectral Correlations

Abstract: Ensembles of quantum chaotic systems are expected to exhibit random matrix universality in their energy spectrum. The presence of this universality can be diagnosed by looking for a linear in time ‘ramp’ in the spectral form factor, but for realistic systems this feature is typically only visible after a sufficiently long time. Given the wide prevalence of this random matrix behavior, it is natural to ask for an effective field theory which predicts the ramp and computes corrections to it arising from physical constraints. I will present such an effective theory based on fluctuating hydrodynamics.

December 1**Xi Yin**, Harvard

Title: Some aspects of D-instantons in string theories

Abstract: I will discuss the effect of D-instantons in type IIB superstring theory, as well as in the non-critical type 0B string theory. I will present new tests of dualities, some previously unknown pieces of string amplitudes, and comment on the role of string field theory. This is based on upcoming works with Agmon, Balthazar, Cho, and Rodriguez.

### String/Gravity Archives

### Spring 2021

February 24

Roberto Emparan

Title: Quantum BTZ black hole

March 3

Kenneth Intriligator, UCSD

Title: RG flows, anomalies, and 2-group global symmetries in 4d and 6d

March 10

Simeon Hellerman, IPMU Tokyo

Title: Quantum Information Theory of the Gravitational Anomaly

March 17

Dieter Luest, LMU Munich

Title: The swampland at a large number of space-time dimensions

March 24

Yasunori Lee, IPMU

Title: Some comments on 6d global gauge anomalies

March 31

Edgar Shaghoulian

April 7

Jorrit Kruthoff, Stanford

Title: Classical aspects of black hole interiors

April 14

Emily Nardoni, UCLA

Title: From SU(N) Seiberg-Witten Theory to Adjoint QCD

April 21

Suvrat Raju, ICTS

April 28

Alejandra Castro

May 5

Xiaoliang Qi, Stanford

Title: Entanglement island, miracle operators and the firewall

May 12

Dan Freed, UT Austin

May 19

Sergio Hernandez–Cuenca , UCSB