Journal Clubs of Spring 2019

June 7 - Markus Dierigl

Title: Walls of marginal stability and the swampland distance conjecture

Abstract: It was conjectured that for all constant theories of quantum gravity traversing large distances in moduli space leads to the presence of a tower of light states with masses exponentially suppressed in the field distance. This has recently been shown to be realized in complex structure deformations of Calabi-Yau 3-folds. However, the states might become unstable due to the presence of walls of marginal stability. We investigate the analogous tower of states for type IIB on K3 x T^2 with emphasis on the stability of the states in the tower and the position of the wall of marginal stability. In this talk I will give an introduction to the necessary techniques and then apply them to the degenerations of K3 x T^2.

Please add some papers for the discussion!

  1. Observation of thermal Hawking radiation and its temperature in an analogue black hole (Nature) (Ramón Muñoz de Nova, Golubkov, Kolobov, Steinhauer)
  2. Charged Quantum Fields in AdS$_2$ (Anninos, Hofman, Kruthoff)

May 29 - Peng Cheng

Title:Black hole entropy from BMS symmetry

Abstract:A striking feature of black hole thermodynamics is the universality of Bekenstein-Hawking entropy. I will remind you how people use symmetry argument, usually conformal symmetry, to reproduce the Bekenstein-Hawking entropy in the next string JC. And then I will mainly focus on the more recently proposed BMS symmetry and show you how this symmetry is strong enough to determine the black hole entropy in a more general setting.

and we discussed

  1. Thermal transitions of metastable M-branes (Armas, Nguyen, Niarchos, Obers)
  2. Back(reaction) to the Future in the Unruh-de Sitter State (Aalsma, Parikh, van der Schaar)
  3. Low-dimensional de Sitter quantum gravity (Jordan Cotler, Kristan Jensen, Alexander Maloney)
  4. Entanglement Wedge Reconstruction and the Information Paradox (Penington)
  5. The entropy of bulk quantum fields and the entanglement wedge of an evaporating black hole (Almheiri, Engelhardt, Marolf, Maxfield)

May 22 - Dora Nikolakopoulou

Title: Traversable wormholes in AdS and bounds on information transfer

Abstract: Recently the discussion about traversable wormholes regained attention due to the construction of a traversable wormhole in AdS, by Gao, Jafferis and Wall. In my talk I will review this construction and I will present an estimate on the maximum number of signals that we can send through.

and we discussed

  1. Real-Time Corrections to the Effective Potential (Pimentel, Stout)
  2. Weak Gravity Conjecture, Black Hole Entropy, and Modular Invariance (Aalsma, Cole, Shiu)
  3. The Complexity Geometry of a Single Qubit (Brown, Susskind)

May 10: Carlos Duaso Pueyo

Title: Positivity Bounds and the Weak Gravity Conjecture
Abstract: The swampland program tries to find criteria to tell whether an EFT can or cannot be consistently embedded into quantum gravity. In this context, it is known that the analytic properties of the UV S-matrix can be used to derive positivity bounds for a set of low-energy EFT operators. I will explain how Bellazzini, Lewandowski and Serra (arXiv:1902.03250) have used this technology to provide positivity constraints for 4D EFTs that contain a massless graviton in the spectrum. In the particular case of Einstein-Maxwell theory, these bounds modify the black hole extremality condition in such a way that the mild form of the Weak Gravity Conjeture is satisfied.

and we discussed:

  1. Sphere Packing and Quantum Gravity (Hartman, Mazáč, Rastelli)
  2. An exact quantization of Jackiw-Teitelboim gravity (Iliesiu, Pufu, Verlinde, Wang)

May 3: Gabriele Sgroi

Title: Logarithmic conformal field theories in 2D
Abstract: Conformal field theories containing reducible indecomposable representations of their chiral algebra are usually called logarithmic conformal field theory because they exhibit logarithmic singularities in their correlation functions. Although far less understood than the standard "rational" case, they are of interest to a wide spectrum of fields ranging from condensed matter theory to string theory and pure math. In the journal club, I will give a brief introduction to the basics of the subject and present a didactical example of such theories.

and we discussed

  1. Einstein gravity from ANEC correlators (Belin, Hofman, Mathys)
  2. Symmetries Near the Horizon (Lin, Maldacena and Zhao)

Apr 24: Ricardo Espindola

Title: Membrane/Gravity duality at large D
Abstract: Several features of black hole dynamics simplify in the limit of large number of space-time dimensions D. In particular, the gravity field localizes in the region near the horizon (the membrane region). The effective non-linear dynamics of light quasi normal modes supported on this region can be described by a probe membrane propagating in a space-time background that solves Einstein’s equations. More recently, an action functional of the membrane shape has been proposed. Such action reproduces the thermodynamics of Schwarzschild black holes even at finite D. I will discuss these ideas during the talk.

and there was no paper discussion since it was a Wednesday

Apr 17: Faculty Corner: Jan Pieter van der Schaar

Title: On States, Singularities and Stability in de Sitter Space
Abstract: The plan is to introduce and discuss some ideas and results on de Sitter physics from an effective field theory point of view. After providing the relevant context, I will analyze a tractable 2d case, pointing out the analogies and differences with respect to black holes. I will end with a discussion on the potential implications for 4d de Sitter space and inflationary cosmology.

We had no paper discussion because it was a longer 1:30h talk.

Apr 12: Lars Aalsma

Title: Positivity Constraints from Black Hole Entropy
Abstract: Not all possible EFTs admit consistent UV completions. Distinguishing what constraints this imposes on higher-dimensional operators in low-energy EFTs has recently seen a revival in the context of the swampland program. In this talk, I will present new constraints derived in a paper from last year by Cheung, Liu and Remmen (https://arxiv.org/abs/1801.08546). They showed that - under certain assumptions - higher-dimensional operators contribute positively to black hole entropy, constraining the sign of the coefficients of higher-dimensional operators. Focussing on Reissner-Nordström black holes, this implies that the charge-to-mass ratio of extremal black holes increases as a function of decreasing mass which serves as a proof of the mild form of the Weak Gravity Conjecture.

and we discussed:

  1. Creating a Traversable Wormhole (Horowitz, Marolf, Santos, Wang)
  2. The First Law of Complexity (Bernamonti, Galli, Hernandez, Myers, Ruan, Simón)
  3. Spacetime Equilibrium at Negative Temperature and the Attraction of Gravity (Jacobson, Visser)
  4. Gravity between Newton and Einstein (Hansen, Hartong, Obers)

Apr 5: Evita Verheijden

Title: A Holographic Argument for the Penrose Inequality in AdS
Abstract: The Penrose Inequality is a test for the weak cosmic censorship conjecture. For asymptotically flat initial data, it gives a lower bound on the mass in terms of the area of apparent horizons. In a recent paper (1903.00555) Engelhardt and Horowitz gave a holographic argument for the Penrose Inequality in AdS. In my talk, I will first discuss the derivation of the original Penrose Inequality and its relation to cosmic censorship. Then I will state the AdS Penrose Inequality and review the new holographic argument. If time allows, we can talk about an interesting connection to the weak gravity conjecture.

and we discussed

  1. JT gravity as a matrix integral (Saad, Shenker, Stanford)
  2. Two dimensional nearly de Sitter gravity (Maldacena, Turiaci, Yang)

Mar 27: Jorrit Kruthoff

Title: In search of de Sitter spacetimes
Abstract: I want to know a bit more about the status of de Sitter solutions in string theory, so that is what I will talk about on Wednesday.

and we had no paper discussion because it was a Wednesday.

Mar 19: Manus Visser

Title: Gravitational Thermodynamics of Causal Diamonds in (A)dS
Abstract: I will talk about my recent paper 1812.01596 with T.Jacobson. We establish a Smarr formula for maximally symmetric diamonds and a "first law" for variations to nearby solutions. The latter relates the variations of the bounding area, spatial volume of the maximal slice, cosmological constant, and matter Hamiltonian. To interpret the first law as a thermodynamic relation, it appears necessary to attribute a negative temperature to the diamond, as has been previously suggested for the special case of the static patch of de Sitter spacetime. With quantum corrections included, for small diamonds we recover the "entanglement equilibrium" result that the generalized entropy is stationary at the maximally symmetric vacuum at fixed volume, and we reformulate this as the extremization of conformal free energy with the volume not fixed.

and we discussed

  1. A Modular Sewing Kit for Entanglement Wedges (Czech, de Boer, Ge, Lamprou)
  2. A Lorentzian inversion formula for defect CFT (Liendo, Linke, Schomerus)

Mar 15: Beatrix Muhlmann
Title: A boundary action for pure AdS3
Abstract: In my talk I will present how J. Cotler and K. Jensen (1808.03263) address the question of finding a boundary action for AdS3. In the first part of my talk I will sketch the derivation. Starting from global AdS3 I will explain how to find a 2 dimensional version of the Schwarzian. In the second part I will tell you how this action is related to the coadjoint orbits of the Virasoro group. Finally I will give some physical applications of the theory derived in the first part.

and we discussed

  1. Lessons on Eternal Traversable Wormholes in AdS (Ben Freivogel, Victor Godet, Edward Morvan, Juan F. Pedraza, Antonio Rotundo)
  2. Firewalls vs Srambling (Yoshida)
  3. Kac-Moody and Virasoro Characters from the Perturbative Chern-Simons Path Integral (Massimo Porrati, Cedric Yu)

Mar 8: Greg Mathys

Title: A bound on Thermal Relativistic Correlators at Large Spacelike Momenta
Abstract: In this journal club, I will talk about a recent paper (1902.07203) where a bound on thermal relativistic correlators at large spacelike momenta is derived. In this limit and with fixed frequency, the size of these correlators is bounded by a geometrical quantity. I will show how to obtain this bound and show that perturbative quantum field theories can saturate this bound at some order in the series. If time allows, I will discuss what happens to the bound in holographic theory.

and we discussed

  1. Clocks and Rods in Jackiw-Teitelboim Quantum Gravity (Blommaert, Mertens, Verschelde)
  2. Holographic CFT states for localized perturbations to AdS black holes (Hong Zhe Chen and Mark Van Raamsdonk)
  3. Eigenstate Thermalisation in the conformal Sachdev-Ye-Kitaev model: an analytic approach (Pranjal Nayak, Julian Sonner, Manuel Vielma)

Mar 1: Antonio Rotundo

Title: A ramp in SYK
Abstract: Black holes are quantum chaotic systems. Their spectrum is discrete and should obey random matrix statistics. Finding signature of this fine grained structure in semiclassical gravity is still an open problem. In a recent paper (1806.06840) Saad, Shenker and Stanford have begun to address this question in the context of SYK and JT gravity. They study the spectral form factor, a quantity that according to random matrix theory has a distinctive late time behaviour, consisting of a ramp and a plateau. They manage to reproduce the ramp using collective variables in SYK and in JT gravity. I will sketch their analysis of SYK and time permitting say a little bit about the JT gravity counterpart.

and we discussed

  1. Observational Signatures of Quantum Gravity in Interferometers (Erik P. Verlinde, Kathryn M. Zurek)
  2. Sphere partition functions & cut-off AdS (Pawel Caputa, Shouvik Datta, and Vasudev Shyam)
  3. Clocks and Rods in Jackiw-Teitelboim Quantum Gravity (Blommaert, Mertens, Verschelde)

Feb 20: Gui Pimentel

Title: Restrictions on Massless S-matrices
Abstract: This talk is largely based on other people’s work (Benincasa, Cachazo; McGady, Rodina). I will show how requirements of locality, unitarity and symmetry put restrictions on the S-matrix of massless particles in flat space. I will also comment on my cosmological motivations for revisiting these works.

and there was no paper discussion since it was a Wednesday

Feb 15: Sagar Lokhande

Title : A Ladder Identity in the SYK Model
Abstract: In this retro-version of the journal club, I will talk about an interesting identity in the SYK model relating the coefficient and the exponent of an out-of-time-order correlator (OTOC). I will begin with a brief review of the model, followed by a discussion of how to calculate a OTOC. Then, I will present the identity and sketch its derivation. I will conclude with brief comments about applications of the identity. This talk is mainly based on the papers: 1812.00120, 1711.08467 and 1604.07818.

and we discussed

  1. Understanding KKLT from a 10d perspective (Yuta Hamada, Arthur Hebecker, Gary Shiu, Pablo Soler) + related 1902.01415 and 1902.01412

Feb 8: Marcos Crichigno

Title: 5d partiton functions with A twist
Abstract: In this talk I’ll tell you about our latest work, in which we compute the exact partition function of 5d N=1 theories on various manifolds. I'll discuss two applications of our results: 1) In the case of 5d maximal SYM this leads to a novel way to compute superconformal index of non-Lagrangian 4d theories, providing a detailed test of a conjecture by Douglas; and 2) In the case of Seiberg theories this leads, via holography, to a microscopic derivation of the entropy of black holes in AdS_6.

and we discussed

  1. Symmetry Breaking in Coupled SYK or Tensor Models (Kim, Klebanov, Tarnopolsky, Zhao)
  2. Kerr-Newman Black Hole Entropy and Soft Hair (Haco, Perry, Strominger)
  3. Higher derivative corrections to Kerr black hole thermodynamics (Reall, Santos)

Feb 1: Jay Armas

Title: Non-extremal brane effective actions and meta-stable states
Abstract: I will explain the method by which non-extremal brane effective actions can be constructed in the supergravity regime. These actions take into account the thermal degrees of freedom of the brane, and can be viewed as describing the equilibrium states of higher-form fluids with multiple conserved currents. I will then explain that finding equilibrium configurations is equivalent to perturbatively finding stationary black hole solutions. As an example, I will discuss how this point of view helped understanding the supergravity dual of non-extremal anti-D3 branes placed at the tip of the Klebanov-Strassler solution, which is a black hole with R^3 X S^2 X S^3 horizon topology. If time permits, I will discuss new results on anti-M2-M5 brane states in M-theory.
Based on arXiv:1812.01067 and related/upcoming works.

and we discussed

  1. Probing typical black hole microstates (Erik, Jan, Sagar et al)
  2. Instabilities of Thin Black Rings: Closing the Gap (Jay et al)
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