Inward Bound - Conference on Black Holes and Emergent Spacetime

17 Aug 2016, 08:00 → 20 Aug 2016, 12:00 Europe/Stockholm

Wallenbergsalen (Nordita, Stockholm)

Bo Sundborg, Lárus Thorlacius, Monica Guica, Niels Obers

Venue

Wallenbergsalen, on the Stockholm University Kräftriket campus, Stockholm, Sweden.

Directions to Wallenbergsalen from Nordita and the hotels

Directions to the Museum of Modern Art, for the dinner on riday evening

Scope

This conference is organized in connection with the Nordita program Black Holes and Emergent Spacetime. The conference will provide a forum for discussing recent advances in gravitational theory and its interplay with quantum theory, with a focus on quantum aspects of black holes and the holographic nature of space-time.

International Advisory Committee

Jan de Boer, University of Amsterdam Charlotte Kristjansen, University of Copenhagen Bengt Nilsson, Chalmers University Ashoke Sen, Harish-Chandra Research Institute

Andrew Strominger, Harvard University Leonard Susskind, Stanford University Marika Taylor, University of Southampton Herman Verlinde, Princeton University

Invited Speakers

Jan de Boer, University of Amsterdam Mirjam Cvetic, University of Pennsylvania Thomas Hartman, Cornell University, USA Gary Horowitz, University of California Santa Barbara, USA Veronika Hubeny, UC Davis, USA Daniel Jafferis, Harvard University, USA David Lowe, Brown University, USA Shiraz Minwalla, Tata Institute for Fundamental Research, India

Kyriakos Papododimas, CERN Theory Division, Switzerland Mukund Rangamani, UC Davis, USA Eva Silverstein, Stanford University, USA Andrew Strominger, Harvard University Marika Taylor, University of Southampton Gerhard 't Hooft, Utrecht University, Netherlands Erik Verlinde, University of Amsterdam, Netherlands Herman Verlinde, Princeton University

Contributed talks

In addition to the invited presentations, there will be a limited number of contributed talks. If you are interested in giving a talk, please mark the corresponding field in the application form and provide a title and abstract in the space provided. You will be notified shortly after the registration deadline whether your talk has been selected.

Slides from talks

Format

There will be three full days of talks followed by a half day on Saturday morning.

Timetable

Registration

If you want to register for the conference, please go to the application form. Due to space restrictions, the total number of participants may have to be limited. Please note that participants attending the Nordita program on Black Holes and Emergent Spacetime during the dates of the conference are automatically registered for participation.

Registration deadline: July 1, 2016

There is no registration fee.

Accommodation

Reduced rates will be available at Arcadia Hotel and BizApartments. In order to get the reduced rate, please mention that you are participating in a Nordita event when making your reservation.

Sponsored by:

Supported by the Royal Swedish Academy of Sciences through its Nobel Institute for Physics

Wednesday, 17 August

1 Registration

2 Welcome from Nordita Director

Speaker: Prof. Hans Hansson (Nordita)

3 Soft hair on black holes

The discovery of an infinite number of new exact conservation laws in all gauge and gravitational theories is reviewed and its implications for black hole information are explored.

Speaker: Andrew Strominger (Harvard University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-strominger.pdf

4 Coffee break

5 Causality in conformal field theory and constraints on graviton couplings

Causality imposes subtle constraints on the coupling constants in effective field theory. If the constraints are violated, then the theory cannot be UV completed. I will describe analogous causality constraints in strongly coupled conformal field theory using the conformal bootstrap. I will also discuss the consequences for the dual gravitational action, and progress towards a direct derivation of Einstein gravity 3-point couplings from CFT.

Speaker: Thomas Hartman (Cornell University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-hartman.pdf

6 A CFT perspective on the black hole interior

In this talk, I present an intrinsic CFT construction of local bulk operators in terms of cross cap boundary states. I discuss how background independence and bulk locality naturally emerge from conformal invariance and the conformal bootstrap. I then describe what it means for one of these bulk observables to cross a black hole horizon.

Speaker: Herman Verlinde (Princeton University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-h_verlinde.pdf

7 Lunch break

8 Effective black hole degrees of freedom at low frequencies

A black hole moving through a slowly varying background can be replaced by a point particle together with some effective interactions with the background by using the (non-quantum) effective field theory method. Some of the coefficients in the so-defined effective black hole (BH) action are known, and in particular 4d Schwarzschild black holes are known to have no induced gravitational polarization at the linearized response level. The BH effective action includes also certain well-defined degrees of freedom whose physical interpretation will be discussed.

Speaker: Barak Kol (Hebrew University)

9 Gravity waves from plunges into black holes via Kerr/CFT

Massive objects orbiting a near-extreme Kerr black hole plunge into the horizon after passing the innermost stable circular orbit, producing an observable signal of gravitational radiation. The near horizon dynamics of such rapidly rotating black holes is governed by a conformal symmetry. In the talk I will show how this symmetry can be exploited to analytically compute the outgoing gravity wave signal for a variety of orbits. I will also discuss the holographic interpretation of the process.

Speaker: Shahar Hadar (DAMTP, University of Cambridge)

10 Effective theories for the dynamics of black branes in supergravity

In certain regimes, perturbations of black branes are described by effective theories of fluid and elastic dynamics. I present recent results on a general account of the dynamics of black branes in supergravity theories, including any type of brane bound state. The type of theories that arise from this analysis are novel types of forced fluid dynamics living on dynamical hypersurfaces, which include force terms due to the presence of Chern-Simons couplings in the supergravity actions. I highlight the relevance of this work for the existence of probe brane configurations in arbitrary supergravity backgrounds with fluxes. Furthermore, I will discuss the connections between these effective theories and the DBI action.

Speaker: Jay Armas (ULB)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-armas.pdf

11 Coffee break

12 Constraining the bulk with boundary causality

In gauge/gravity duality, points which are not causally related on the boundary cannot be causality related through the bulk; this is the statement of boundary causality. This requirement constrains the behavior of perturbative quantum corrections to the bulk geometry. I will present a (background-dependent) bulk condition which is both necessary and sufficient to guarantee boundary causality. This constraint is less restrictive than the Averaged Null Energy Condition in the bulk.

Speaker: Netta Engelhardt (University of California Santa Barbara)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-engelhardt.pdf

13 Precursors, gauge invariance, and quantum error correction in AdS/CFT

A puzzling aspect of the AdS/CFT correspondence is that a single bulk operator can be mapped to multiple different boundary operators, or precursors. By improving upon a recent model of Mintun, Polchinski, and Rosenhaus, I demonstrate explicitly how this ambiguity arises in a simple model of the field theory. In particular, I show how gauge invariance in the boundary theory manifests as a freedom in the smearing function used in the bulk-boundary mapping, and explicitly show how this freedom can be used to localize the precursor in different spatial regions. I also show how the ambiguity can be understood in terms of quantum error correction, by appealing to the entanglement present in the CFT. The concordance of these two approaches suggests that gauge invariance and entanglement in the boundary field theory are intimately connected to the reconstruction of local operators in the dual spacetime.

Speaker: Laurens Kabir (University of Amsterdam)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-kabir.pdf

14 The weak gravity conjecture in three dimensions

The Weak Gravity Conjecture (WGC) predicts the existence of light charged states in any weakly couple gauge theory also coupled to gravity, which have been shown to have crucial consequences to e.g. Large field inflation models. In spite of the abundance of evidence for the conjecture both via black hole decay arguments and a plethora of concrete examples in String Theory, no formal proof of the WGC has been produced so far. We will provide such a proof in the restricted case of AdS3 spacetimes, using modular invariance of the dual CFT. Notably, most of the WGC heuristics based on black hole evaporation do not apply here. We also discuss an interesting discrete charge which arises naturally in our discussion, for which modular invariance is not enough to show the existence of light charged states. This discrete symmetry manifests itself as discrete electric hair on BTZ black holes.

Speaker: Miguel Montero (Instituto de Fisica Teorica UAM-CSIC)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-montero.pdf

15 Break

16 Holographic black hole chemistry

Thermodynamic quantities associated with black holes in Anti-de Sitter space obey an interesting identity when the cosmological constant is included as one of the dynamical variables: the generalized Smarr formula. This relation can be shown to follow from relatively simple considerations in the dual holographic field theory. The large N behavior of extensive thermodynamics quantities in the gauge theory yield a universal relation from which, with additional input, the generalized Smarr formula naturally follows.

Speaker: Brandon Robinson (University of Washington)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-robinson.pdf

17 Glimpses of black hole formation/evaporation in highly inelastic, transplanckian energy string collisions

We revisit possible glimpses of black-hole formation by looking at trans-planckian string-string collisions at very high final-state multiplicity. We compare, in particular, previous results using the optical theorem, the resummation of ladder diagrams at arbitrary loop order, and the AGK cutting rules, with the more recent study of 2 → N scatterings. We argue that some apparent tension between the two approaches disappears once a reinterpretation of the results in the latter approach is adopted. Under that assumption, the typical final state produced in a highly trans- planckian collision does indeed appear to share some properties with those expected from the evaporation of a black hole of mass √s, although no sign of thermalization is seen to emerge at this level of approximation.

Speaker: Andrea Addazi (UNIVAQ, LNGS INFN)

18 Collisions of pointlike particles in three-dimensional anti-deSitter space

We study collisions of many point-like particles in three dimensional anti-de Sitter space, generalizing the known result with two particles. We show how to construct exact solutions corresponding to the formation of either a black hole or a conical singularity from the collision of an arbitrary number of massless particles falling in radially from the boundary. We find that when going away from the case of discrete rotational symmetry, this is not a trivial generalization of the two-particle case, but requires that the excised wedges corresponding to the particles must be chosen in a very precise way for a consistent solution. We also explicitly take the limit when the number of particles goes to infinity and obtain thin shell solutions that in general break rotational invariance, corresponding to an instantaneous and inhomogeneous perturbation at the boundary. We also compute the stress-energy tensor of the shell using the junction formalism for null shells and obtain agreement with the point particle picture.

Speaker: Jonathan Lindgren (VUB)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-lindgren.pdf

19 Welcome reception

Thursday, 18 August

20 Holography inside the horizon

Issues with the construction of black hole interiors in holographic theories are reviewed, and a solution is presented. Key ingredients are the role of the ultraviolet cutoff on the gravity side, and the identification of decoherence of interior degrees of freedom with singularity approach.

Speaker: David Lowe (Brown University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-lowe.pdf

21 Renormalisation of entanglement entropy

In this talk we will discuss how entanglement entropy can be renormalised, both holographically and in field theory.

Speaker: Marika Taylor (Mathematical Sciences, University of Southampton)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-taylor.pdf

22 Coffee break

23 The black hole as a hydrogen atom

Three important insights are needed to understand black holes, conservation of information, complementarity and firewalls. One: the gravitational force between in- and out-going particles, two: the spherical wave expansion, and three: antipodal identification. Neglecting any one of these three points turns black holes into complete mysteries, while they can be as transparent as the hydrogen atom. It is shown how every partial wave obeys a very simple, easily solvable, Schroedinger equation (just as in the hydrogen atom), featuring only pure quantum states. However, we do end up doing “new physics”, as soon as we apply the required cut-offs at the Planck scale. (The talk will be given via skype).

Speaker: Gerard 't Hooft (Institute for Theoretical Physics, Utrecht University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-thooft.pdf

24 Non-extremal black holes, subtracted geometry and holography

We review the thermodynamic properties of general asymptotically flat black holes in four dimensions, suggestive of a dual conformal field theory interpretation. We introduce the so-called subtracted geometry as an ``asymptotically conical box'' of non-extremal black holes where the conformal symmetry becomes manifest. Employing holographic renormalization techniques in a variational problem in terms of equivalence classes of boundary data under the local asymptotic symmetries of the theory, we derive the conserved charges and the first law of thermodynamics for the subtracted geometry. We also formulate a holographic dictionary for this geometry in terms of a two-dimensional Einstein-Maxwell-Dilaton model.

Speaker: Mirjam Cvetic (University of Pennsylvania)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-cvetic.pdf

25 Lunch break

26 Smooth horizonless geometries deep inside the black-hole regime

The study of black hole microstates in string theory is an important problem, which offers the potential to resolve the information paradox. I will present a new family of D1-D5-P supergravity solutions, whose dual CFT states exhibit the important feature that the momentum charge is fractionated. I will then describe recent work on constructing a more general class of black hole microstate geometries. This class includes solutions that have arbitrarily small angular momenta, deep within the regime of quantum numbers and couplings for which a large classical black hole exists. I will close with a discussion of the physics of an observer falling into a black hole.

Speaker: David Turton (CEA Saclay)

27 Quantum tunneling and black hole horizons

To unify quantum mechanics and general relativity it has been argued that effective field theory has to break down at the horizon of black holes. To establish this premature breakdown of general relativity a dynamical mechanism needs to be provided. I will discuss the possibility of quantum tunneling as a means to avoid the formation of a horizon in the gravitational collapse process. Surprisingly, the amplitude to tunnel into microstate geometries built from key ingredients of string theory - extra dimensions, topology and fluxes - is not parametrically suppressed.

Speaker: Andrea Puhm (UC Santa Barbara)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-puhm.pdf

28 AdS black holes and baryonic charges

This talk deals with AdS black holes arising as solutions of four dimensional supergravity admitting an embedding in M-theory. Supersymmetric AdS4 black holes with spherical horizon were discovered quite recently and have lately attracted some attention, given that their entropy was successfully reproduced via the computation of the twisted Witten index in ABJM theory. After reviewing recent progress in the analysis of supersymmetric and non supersymmetric configurations, I will discuss some ongoing work on a class of new solutions arising from M-theory on 7d Sasaki-Einstein coset manifolds. Such thermal black holes are characterized by charged scalars and massive vector fields. The analysis of the stability of probes in such a background gives insight on the possible existence of stable of multi-center black holes in anti-de Sitter, relevant for the holographic description of the glass phase transition.

Speaker: Chiara Toldo (Columbia University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-toldo.pdf

29 Coffee break

30 A toy model of black hole complementarity

We consider the algebra of simple operators defined in a time band in a CFT with a holographic dual. The action of these operators on the CFT vacuum can generate all low energy states in the CFT, and no operator within the algebra can annihilate the vacuum. For a time band smaller than the light crossing time of AdS, local excitations within the causal diamond in the centre of AdS are invisible to the algebra of simple operators on the boundary by causality. However, we show that if one goes beyond this algebra by considering all possible boundary operators inside the time band, it is possible to reconstruct local physics inside the diamond as well. Our construction therefore provides a toy model of black hole complementarity. This not only proves that such non-locality is a fundamental feature of quantum gravity that holds even in empty space, but also shows that the distinction between simple and complicated operators is a crucial feature of the approximate emergence of locality.

Speaker: Souvik Banerjee (Groningen University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-banerjee.pdf

31 Extended black hole and entanglement thermodynamics in holography

I will review recent results on extending the laws of black hole thermodynamics where the gravity couplings are treated as additional thermodynamic variables. In the holographic context, varying these couplings can be interpreted as inducing an RG-flow in the space of field theories, with monotonicity theorems and associated phase transitions. In the second part of this talk I will present the extended laws of entanglement entropy that can be derived in this context. I will show that the extra contributions to the entanglement can capture additional information of the bulk theory that is not available in the standard formalism.

Speaker: Juan Pedraza (University of Amsterdam)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-pedraza.pdf

Friday, 19 August

32 Recovering the spacetime metric from a holographic dual

Consider any asymptotically AdS spacetime. We introduce a special class of spacelike cross-sections of the boundary called light-cone cuts. We will first show that the conformal metric in the bulk (i.e. the metric up to an overall conformal factor) can be reconstructed just from the location of these cuts. We then show how the light-cone cuts can be determined from the dual field theory. Finally we show how (at least in some cases) the conformal factor can also be determined. This provides a new approach to determining the bulk geometry from the dual field theory. These results were obtained in collaboration with Netta Engelhardt.

Speaker: Gary Horowitz (UC Santa Barbara)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-horowitz.pdf

33 Entanglement holography

Speaker: Jan de Boer (University of Amsterdam)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-deboer.pdf

34 Coffee break

35 Long-range longitudinal string spreading at six points: simulation of horizon infallers

We analyze a tree-level six point scattering process in which two strings are separated longitudinally such that they could only interact directly via a non-local spreading effect such as that predicted by light cone gauge calculations and the Gross-Mende saddle point. One string, the `detector', is produced at a finite time with energy $E$ by an auxiliary $2\to 2$ sub-process, with kinematics such that it has sufficient resolution to detect the longitudinal spreading of an additional incoming string, the `source'. We test this hypothesis in a gauge-invariant S-matrix calculation convolved with an appropriate wavepacket, discussing several interesting subtleties in the calculation and interpretation. The amplitude exhibits support spread over the predicted large longitudinal separation $\sim\alpha' E$ between the central trajectories of the strings, simulating a comparable interaction between time-translated horizon infallers. This effect results from the inherent UV softness of string amplitudes, in sharp contrast to tree-level quantum field theory in a similar kinematic regime.

Speaker: Eva Silverstein (Stanford University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-silverstein.pdf

36 The black hole membrane at large D

Speaker: Shiraz Minwalla (TIFR, Mumbai)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-minwalla.pdf

37 Lunch break

38 BMS vacua and black holes

I will present a construction of bms representations in the bulk spacetime for stationary metrics. I will discuss the resulting properties of the Poincare invariant vacua and the Schwarzschild black hole with BMS hair.

Speaker: Geoffrey Compere (ULB)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-compere.pdf

39 Boundary causality vs hyperbolicity for small black Holes in Gauss-Bonnet

Both boundary CFT causality and hyperbolicity of the bulk equations of motion constrain the coupling constant for Gauss-Bonnet gravity. We study these constraints for small black holes in AdS5. If we rule out solutions that violate local hyperbolicity via a `hyperbolicity censorship hypothesis', then we find the parameter space is not restricted beyond the $\lambda \lesssim 9/100$ limit from planar black holes.

Speaker: Cynthia Keeler (Niels Bohr Institute)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-keeler.pdf

40 Three-dimensional conformal higher spin theory

We analyse the non-linear frame field theory of conformal higher spins in three dimensions via its Chern-Simons formulation. Its relation to the metric formulation is explained. The full non-linear spin 3 Cotton equation with spin 4 fields and higher truncated away is derived. The coupling to scalar fields (AdS4 singletons) is given in terms of a star product unfolded equation. The reason for studying theories of this kind come from AdS4/CFT3 with Neumann boundary conditions for gauge fields in AdS4.

Speaker: Bengt Nilsson (Chalmers University of Technology)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-nilsson.pdf

41 Coffee break

42 New modes from higher curvature corrections in holography

In gravitational theories involving higher curvature corrections the metric describes additional degrees of freedom beyond the graviton. Holographic duality maps these to operators in the dual CFT. We identify infinite families of theories for which these new modes cannot be truncated and the usual Fefferman-Graham expansion needs to be modified. New massive gravity in three dimensions and critical gravity in four dimensions are particular representatives of these families. We propose modified expansion, study the near-boundary behaviour of the metric and derive fall-off properties of the additional modes in theories involving higher derivative corrections. Based on http://arxiv.org/abs/1511.08747.

Speaker: Yegor Korovin (Albert Einstein Institute)

43 Towards higher spin bulk reconstruction from thermal O(N) correlators

A free O(N) vector model on a sphere has been conjectured to be dual to a higher spin theory on an AdS background. It displays an interesting thermal structure with a phase transition at temperatures of order \sqrt{N}. We attempt to shed further light on the nature of this phase transition by considering thermal correlation functions of singlet operators in the CFT. Above the transition an additional length scale emerges, below which the behavior tracks that of a free theory, exhibiting a characteristic logarithmic scaling with distance. At larger distances, the scaling returns to that of the low energy phase. We then provide a first attempt at a geometrical interpretation of this behavior and outline a method to reconstruct the dominant bulk geometry from the behavior of the correlators.

Speaker: Irene Amado (Stockholm U.)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-amado.pdf

44 Buffet reception

Saturday, 20 August

45 Covariant entanglement constructs

To elucidate the AdS/CFT dictionary, it is useful to consider fully general time-dependent situations, and use general covariance as a guide in constructing a map. One particularly interesting quantity, potentially revealing the underlying structure of bulk geometry, is entanglement. In case of holographic entanglement entropy in static situations, Headrick and Freedman have recently proposed an alternative to the Ryu-Takayanagi (entanglement entropy = minimal surface area) prescription. In this talk I will discuss covariant versions of this proposal.

Speaker: Veronika Hubeny (UC Davis)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-hubeny.pdf

46 A new perspective on the Schwinger-Keldysh formalism

I will describe how the Schwinger-Keldysh formalism which is geared for computing time-ordered correlation functions in relativistic QFTs admits a set of topological symmetries. We will explore these symmetries for near-thermal systems and explain how they are useful in constraining low energy dynamics. We will specifically look at the construction of hydrodynamic effective field theories. Time permitting we will also touch upon other potential applications.

Speaker: Mukund Rangamani (UC Davis)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-rangamani.pdf

47 Coffee break

48 Traversable wormholes via a double trace deformation

Speaker: Daniel Jafferis (Harvard University)

slides http://www.nordita.org/docs/agenda/slides-bh2016c-jafferis.pdf

49 Emergent gravity in de Sitter space.

In Anti-de Sitter space the emergence of gravity relies on the area law for entanglement entropy. Using insights from tensor networks and string theory we argue that de Sitter space contains a volume law contribution to the entropy, which overtakes the area law precisely at the cosmological horizon. Due the competition between area and volume law entanglement the microscopic states do not thermalise at sub-Hubble scales. When matter is included, this causes a memory effect in the form of an displacement of the entropy density. As a result the emergent laws of gravity contain, in addition to the familiar force law, an `elastic response' due to the entropy displacement. We estimate the strength of this extra `dark gravitational force' in terms the (baryonic) mass and the Hubble acceleration scale, and find good agreement with observed phenomena in galaxies and clusters.

Speaker: Erik Verlinde (University of Amsterdam)