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UvA Strings Journal Club Wiki


Here we will keep a list of papers for discussion at the journal club. If you see a paper that seems interesting during the week (up to Wed), just add it to the list and the organizer (i.e. Damian) will bring it up during the journal club on Friday. The Edit button is in the drop-down menu that appears if you click the arrow on the top right.

THIS WEEK

April 25: John Stout

Title: Toy Models for Axion Dynamics

Abstract: An axion enjoys a perturbatively exact continuous shift symmetry, which may be broken down to a discrete shift symmetry by nonperturbative effects---e.g. gauge theory instantons. This exact discrete shift symmetry makes the axion a promising inflaton candidate, wherein the axion is imagined to roll down its nonperturbatively-generated quantum effective potential. While the effective potential is a very useful tool for studying the vacuum structure of a quantum theory, it is unclear when (or if) it can be applied to time-dependent situations or how instantons behave in time-dependent backgrounds. In this talk, I will describe some work in progress towards understanding these questions in toy quantum mechanical models.
NEXT WEEK

No Journal Club next week (We will have a seminar by Tolya Dymarsky instead)

and we will discuss:

1. An N=1 3d-3d Correspondence (Eckhard, Schaefer-Nameki, Wong)
2.



Journal Clubs of the Recent Past

April 18: Cesar Agon (YITP, Stony Brook)
(no papers discussion)

Title: Subsystem Complexity and Holography

Abstract: I will review pure state complexity and some of the motivations that lead to the two latest versions for its holographic duals, which are quoted as "complexity equals volume" and "complexity equals action". In that context I will present some holographic calculations of what has been suggested to be the dual to subsystem complexity and proposed some candidate definitions for the subsystem complexity in the context of quantum information. Finally, using some intuition from tensor networks I will try to argue in favor of the action proposal for the complexity of subsystems. The presentation will be restricted to the context of the thermal field double state, where the subsystem corresponds to the thermal density matrix of a single CFT.

April 13: Gui Pimentel

Title: Cosmological Correlators from the Boundary

Abstract: I will describe how to compute cosmological correlation functions from the point of view of the late time, Hartle-Hawking wavefunction of the universe. I will explain how the features of the wavefunction tell us about new particles that we cannot detect directly, but might have been produced in the early universe.

and we will discuss:

1. The Factorization Problem in Jackiw-Teitelboim Gravity (Harlow and Jafferis)
2. Vacua on the Brink of Decay (Pimentel, Polyakov and Tarnopolsky)

April 6: Adolfo Toloza

Title: Gravity and Elasticity

Abstract: It's very well known the relation between Gravity and Geometry, but what is not that well known is the connection between Elasticity and Geometry. This suggest that, by transitivity, there should be a link between Gravity and Elasticity, where the strain tensor of the solid is identified with the (perturbation of the) metric of space time (i.e. Phonons with Gravitons).

In this Journal Club I will describe the formalism of topological defects in crystals and multivalued fields in gauge theories. I will explain how crystals with defects can be described in terms of a Riemann-Cartan geometry, and the other way around Rieman-Cartan space times can be build from multivalued coordinate transformations of Minkowski space time.

and we will discuss:
1. The Factorization Problem in Jackiw-Teitelboim Gravity (Harlow and Jafferis)
2. Airy Function and 4D Quantum Gravity( Caputa, Hirano)
3. What if string theory has no de Sitter vacua? (Danielsson, van Riet)
4. Subsystem Complexity and Holography (Agon, Headrick, Swingle)
5. Loops in Anti-de Sitter Space (Bertan, Sachs)

March 28: Lars Aalsma

Title: Spontaneous supersymmetry breaking in string theory

Abstract:
In order to obtain de Sitter vacua from string theory, we have to break supersymmetry. Anti-branes are a popular way of breaking supersymmetry and they are a crucial step in many constructions of de Sitter vacua from string theory. In this talk, I will describe how anti-branes can break supersymmetry spontaneously and discuss the implications for the effective theory describing this process. This talk will be based on published (https://arxiv.org/abs/1703.05771) and unpublished work together with Jan Pieter van der Schaar, Magnus Tournoy and Bert Vercnocke.

March 21: Jorrit Kruthoff

Title: OPE inversion formula

Abstract: Recently, Simon Caron-Huot derived a formula that turns a CFT four point function in OPE data. I will discuss its derivation, uses and implications.

March 9: Faculty Corner - Ben Freivogel

Title: How to build the thermofield double state
Abstract: I will discuss ongoing work addressing whether there is a simple way to bring two copies of a quantum system into the thermofield double state.

and we will discuss:
1-Emergent gravity from relatively local Hamiltonians and a possible resolution of the black hole information puzzle (Sung-Sik Lee)
2-The Holographic Shape of Entanglement and Einstein's Equations (Aitor and Onkar)
3-Entanglement of Purification in Free Scalar Field Theories (Takayanagi et al)
4-Gravity from entanglement for boundary subregions (Blanco)
5-N=1 dualities in 2+1 dimensions (Benini et al)
6-Thermal Conformal Blocks (Maloney et al)

March 2: Hongliang Jiang

Title: Exact Virasoro Blocks from Wilson Lines
Abstract: I will review the formalism of computing Virasoro blocks exactly in terms of Wilson lines, its verification perturbatively in 1/c, and the physical justification based on Virasoro Ward identity (1612.06385).

and we will discuss:
1- Phase transitions in 3D gravity and fractal dimension (Maloney et al)
2- Deep Learning and AdS/CFT (Hashimoto et al)
3- Emergence and the Swampland Conjectures (Heidenreich, Reece and Rudelius) and Infinite Distances in Field Space and Massless Towers of States (Grimm, Palti and Valenzuela)
4- Goldstone modes and photonization for higher form symmetries (Diego and Nabil)
5- The Conformal Bootstrap at Finite Temperature (DSD, Perlmutter et al)

Feb 21: Sagar F. Lokhande

Title: Smooth AdS black holes, quantum teleportation and quantum chaos
Abstract: In this talk, I would like to share some insights into the geometry of a typical Schwarzschild black hole in AdS spacetime. Such black holes are dual to typical, equilibrium, heavy pure states in the dual CFT. I will first define (at large N) operators in the CFT that probe the interior of the black holes. Then, I will show that a correlator, calculated after a specific double-trace perturbation of the CFT states, can be interpreted as a quantum teleportation out of the black hole. I will provide evidence for the non-vanishing of this correlator. This will take us to a very interesting statement about the growth of general time-dependent correlators in typical vs thermal states in the CFT, which I will present as a conjecture. If time permits, I will discuss some more evidence for the conjecture and semi-analytical calculations in the SYK model. The talk is based on unpublished work with Jan de Boer, Rik van Breukelen, Kyriakos Papadodimas and Erik Verlinde.

Feb 16: Fernando Rejon-Barrera

Title: Weight Shifting Operators and Conformal Blocks
by Denis Karateev, Petr Kravchuk, David Simmons-Duffin
Abstract:
We introduce a large class of conformally-covariant differential
operators and a crossing equation that they obey. Together, these
tools dramatically simplify calculations involving operators with spin
in conformal field theories. As an application, we derive a formula
for a general conformal block (with arbitrary internal and external
representations) in terms of derivatives of blocks for external
scalars. In particular, our formula gives new expressions for "seed
conformal blocks" in 3d and 4d CFTs. We also find simple derivations
of identities between external-scalar blocks with different dimensions
and internal spins. We comment on additional applications, including
derivation of recursion relations for general conformal blocks,
reducing inversion formulae for spinning operators to inversion
formulae for scalars, and deriving identities between general 6j
symbols (Racah-Wigner coefficients/"crossing kernels") of the
conformal group.

and we will discuss:
1- To gauge or not to gauge? (Maldacena, Milekhin)
2- Gauged And Ungauged: A Nonperturbative Test(Hanada et al)
3- Black Holes and Complexity Classes (Susskind)

Feb 9: Victor Godet

Title: Black hole entropy in ABJM theory
Abstract: I will review the microscopic derivation of the Bekenstein-Hawking entropy of AdS4 black holes from supersymmetric localization in ABJM theory (1511.04085).

and we will discuss:
1- Dirichlet-Branes and Ramond-Ramond Charges, Joseph Polchinski.
2- Renormalization and Effective Lagrangians (Joe Polchinski)
3- Why do things fall? (Susskind)

Feb 2: Eva Llabrés

Title: Wilson Lines and Ishibashi states in AdS3/CFT2

Abstract: I will present unpublished work with Alejandra Castro and Nabil Iqbal, in which we provide a refined interpretation of a gravitational Wilson line in AdS3 in terms of Ishibashi states in the dual CFT2. Our strategy is to give a method to evaluate the Wilson line that accounts for all the information contained in the representation, and clarify the role of boundary conditions at the endpoints of the line operator. This gives a novel way to explore and reconstruct the local bulk dynamics which we discuss.

and we will discuss:
1- Proof of the Weak Gravity Conjecture from Black Hole Entropy (Cheung, Liu and Remmen)
2 - Comments on a state-operator correspondence for the torus (Alex, Jan, Jorrit)

January 27: Grant Salton (Stanford)

Title: Entanglement wedge reconstruction via approximate operator algebra quantum error correction

Abstract: Quantum error correction -- originally invented for quantum computing -- has proven itself useful in a variety of non-computational physical systems, as the ideas of QEC are broadly applicable. In this talk, I'll focus on the recent discovery that even the AdS/CFT correspondence implements quantum error correction. We will study the hypothesis that any local bulk operator in AdS can be reconstructed using only a causally disconnected subregion of the CFT (the so-called entanglement wedge reconstruction hypothesis). This hypothesis has been proven correct under the assumption that error correction in AdS/CFT is exact, but this assumption is not expected to hold. Fortunately, recent advances in the theory of approximate quantum error correction have emerged, which can be leveraged to solve this problem. In this talk, we will first review these results on recoverability and approximate quantum error correction, and then we'll learn new generalizations of those ideas to both the case of recovery of quantum subsystems, as well as recovery for algebras of observables. We will then review some basics of AdS/CFT and the entanglement wedge hypothesis. With all these tools in hand, we will prove that entanglement wedge reconstruction can be done robustly, and we'll find an explicit formula for reconstructed bulk operators. Joint work with Jordan Cotler, Patrick Hayden, Brian Swingle, and Michael Walter: https://arxiv.org/abs/1704.05839


and we will discuss:
1- Extremal Tunneling and Anti-de Sitter Instantons (Lars and Jan Pieter)
2- A Local First Law of Gravity (Parikh, Sarkar, Svesko)

January 12: Sam van Leuven

Title: Towards non-AdS Holography via the Long String Phenomenon

Abstract:
In this talk I will present my recent paper with Erik en Manus (https://arxiv.org/abs/1801.02589), whose abstract reads:
The microscopic description of AdS space obeys the holographic principle in the sense that the number of microscopic degrees of freedom is given by the area of the holographic boundary. We assume the same applies to the microscopic holographic theories for non-AdS spacetimes, specifically for Minkowski, de Sitter, and AdS below its curvature radius. By taking general lessons from AdS/CFT we derive the cut-off energy of the holographic theories for these non-AdS geometries. Contrary to AdS/CFT, the excitation energy decreases towards the IR in the bulk, which is related to the negative specific heat of black holes. We construct a conformal mapping between the non-AdS geometries and AdS(3)xS(q) spacetimes, and relate the microscopic properties of the holographic theories for non-AdS spaces to those of symmetric product CFTs. We find that the mechanism responsible for the inversion of the energy-distance relation corresponds to the long string phenomenon. This same mechanism naturally explains the negative specific heat for non-AdS black holes and the smallness of the vacuum energy in (A)dS spacetimes.

and we will be discussing:

1. Logarithmic Corrections to Black Hole Entropy: the Non-BPS Branch (Alejandra, Victor, et al.)
2. Holographic Complexity is non-local (Fu, Maloney, Marolf,et. al.)
3. Double-trace Deformations of Conformal Correlators (Giombi, Kirilin, Perlmutter)
4. Cutoff AdS3 versus the TTbar-deformation (Kraus, Liu and Marolf)



Journal Club Etiquette:

We will have many improvements. The most important ones:

Timing:
A talk is 40 minutes. To allow for questions (during and after the talk), you will be STRICTLY cut off after 45 minutes.
Talks:
the topics should preferably be either own work or a current research theme, rather than one particular paper. Ideas for 'hot topics' for future JC's can be posted here
Other:
- we will stimulate working groups, new collaborations and feedback for speakers
- the moderator will keep a close watch on context and priority of papers on the list
- post papers that appeared the week ending on Wednesday, to allow more reading time.

For more improvements, see the JC Manifesto


Journal Clubs of the Distant Past:

Fall 2017
Spring 2017
Fall 2016
Spring 2016
Fall 2015
Spring 201