A Holographic Sampling

15 May 2017, 09:55 → 16 May 2017, 18:00 Europe/Copenhagen

Auditorium A (Niels Bohr Institute)

This is a mini-workshop at Niels Bohr Institute with several invited experts in Holography each giving their take on the current status of the subject in a one-hour talk. The meeting is organized so that there is ample time for informal discussions and interaction. The experts are:

• Alejandra Castro (Amsterdam)
• Guido Festuccia (Uppsala)
• Finn Larsen (University of Michigan)
• Gim Seng Ng (McGill)
• David Poland (Yale)
• Andrea Puhm (Harvard and CNRS, École Polytechnique)
• Phil Szepietowski (Utrecht)
• Larus Thorlacius (Iceland University and Stockholm University)

Local attendants that would like to participate are encouraged to register.

Non-local participants are welcome to register and participate as well (as long as space permits), but are responsible for making their own hotel arrangements.

After the workshop on Tuesday evening, we will organize a casual excursion to Papirøen, one of Copenhagen's local street food destinations.  Please see http://copenhagenstreetfood.dk/en/ for more information.  Signups will be available during the workshop.

The mini-workshop is made possible with support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Actions. 

Organizers: Cynthia Keeler & Niels Obers
Secretary: Pia Kohring

Monday, 15 May

10:00 → 11:00 Phil Szepietowski: Alternative boundary conditions in AdS, one-loop determinants and WCFTs

I will discuss the computation of the graviton one-loop determinant in the BTZ black hole background with certain chiral boundary conditions at the AdS boundary. These boundary conditions were proposed by Compere, Song and Strominger and were shown to modify the asymptotic symmetry algebra from a sum of left and right Virasoro algebras to a single right-moving Virasoro U(1) Kac-Moody. This implies that the holographic dual description possesses such global symmetry and so should be described by a warped conformal field theory (WCFT) instead of a standard CFT. In the talk I will overview the new boundary conditions and the concept of a WCFT, outline the computational method of obtaining the one-loop determinant from the "quasinormal" mode spectrum (highlighting elements which are unique to the new boundary conditions) and discuss the implications of the results for the boundary field theory.

11:00 → 11:30 Coffee

11:30 → 12:30 Finn Larsen: TBA

12:30 → 14:00 Lunch

14:00 → 15:00 Alejandra Castro: Siegel Modular Forms and Black Hole Entropy

In this talk I will present statistical systems, or more precisely counting formulas, that have the potential to account for the entropy of an extremal black hole. The goal is to capture and translate the robustness in gravity into data of the quantum system. One the microscopic side, which is the main emphasis of this talk, I want to illustrate not only how one can design generating functions with the desired features, but also present a procedure to extract the entropy systematically.

15:00 → 16:00 Coffee

16:00 → 17:00 Guido Festuccia: Supersymmetric Indices and RG Flows

Indices are a powerful tool to analyse the dynamics of supersymmetric field theories; for instance, supersymmetric indices for non-conformal susy field theories can be used to explore their RG flows. An interesting class of indices can be defined by placing (non conformal) supersymmetric field theories on S^dxS^1 preserving susy. For N=1 this index is related to the N=1 superconformal index in a simple way. For N=2 superconformal theories one can also define an index but its extension to non conformal N=2 field theories is not possible. Nevertheless, I will show that a particular limit of the N=2 superconformal index, the "Schur limit", can be defined for non conformal field theories. I will then explore the properties and uses of this index.

Tuesday, 16 May

10:00 → 11:00 Andrea Puhm: A rough end for smooth microstate geometries

The study of supersymmetric black holes in string theory has been a useful arena for the search for the correct microscopic description of black holes, with one of its greatest triumphs being the explicit stringy counting by Strominger and Vafa of the number of microstates of the D1-D5-P system. The fuzzball program is an attempt to describe these microstates at finite coupling with the extended objects of string theory modifying the structure of the black hole horizon by replacing it with an end to spacetime. An important open question is what fraction of these microstates is smooth, contains singularities corresponding to D-brane sources or is arbitrarily quantum and/or strongly curved. Recently Eperon, Reall, and Santos identified a non-linear classical instability in these geometries due to the growth of excitations at an “evanescent ergosurface” of infinite redshift whose implications for the fuzzball program depend crucially on its endpoint. In this talk I will argue that the instability drives rare smooth microstates with large angular momentum to more typical microstates with smaller angular momentum and terminates when the density of microstates is maximal. At this point, the large stringy corrections to such microstates may render them non-linearly stable just as supergravity breaks down: a rough end for smooth microstate geometries. I will discuss a possible mechanism for this stabilization detailed in an illustrative toy model.

11:00 → 11:30 Coffee

11:30 → 12:30 Larus Thorlacius: Probing emergent geometry in free vector and matrix models

Boundary correlation functions provide insight into the emergence of an effective geometry in higher spin gravity duals of O(N) or U(N) symmetric field theories. On a compact manifold, the singlet constraint leads to nontrivial dynamics at finite temperature and large N phase transitions even at vanishing ’t Hooft coupling. At low temperature, the leading behavior of boundary two-point functions is consistent with propagation through a bulk thermal AdS space. Above the phase transition, the two-point function shows significant departure from thermal AdS space and the emergence of localized black hole like objects in the bulk.

12:30 → 14:00 Lunch

14:00 → 15:00 Gim Seng Ng: Witten Diagrams for Torus Conformal Blocks

We give a holographic description of global conformal blocks in two dimensional conformal field theory on the sphere and on the torus. We show that the conformal blocks on the torus can be written as Witten diagrams in the thermal AdS. This is accomplished by deriving a general conformal Casimir equation for global conformal blocks, and showing that Witten diagrams obey the same equation. We study in detail the semi-classical limit, where conformal blocks are given by the action of a network of bulk world-lines obeying appropriate geodesic equations. We give an alternate description in the Chern-Simons formulation of 3D gravity, where the conformal blocks are described by networks of Wilson lines, and show that these formulations are equivalent.

15:00 → 16:00 Coffee

16:00 → 17:00 David Poland: Bootstrapping the Stress-Energy Tensor

I will discuss recent progress at extending the conformal bootstrap to 4-point functions containing the stress-energy tensor. This progress includes deriving analytical sum rules for the coefficients in stress-tensor 2-point and 3-point functions, and producing numerical bounds on these coefficients for various gaps in the spectrum. All of these constraints can be interpreted holographically as highly nontrivial restrictions on the properties of bulk gravity in AdS.