Dinner at Sources

Thermalization and Chaos in 1+1d QFTs

• Luca Delacrétaz (UNIGE)

Nonintegrable QFTs are expected to thermalize and exhibit emergence of hydrodynamics and chaos. In weakly coupled QFTs, kinetic theory captures local thermalization; such a versatile tool is absent away from the perturbative regime. I will present analytical and numerical results using nonperturbative methods to study thermalization at strong coupling. I will show how requiring causality in the thermal state leads to strong analytic constraints on the thermodynamics and out-of-equilibrium properties of any relativistic 1+1d QFT. I will then discuss Lightcone Conformal Truncation (LCT) as a powerful numerical tool to study thermalization of QFTs. Applied to \phi^4 theory in 1+1d, LCT reveals eigenstate thermalization and onset of random matrix universality at any nonzero coupling. Finally, I will discuss prospects for observing the emergence of hydrodynamics in QFTs using Hamiltonian truncation.

How to Compute Nonperturbative Scattering Amplitudes

• Matthew Thomas Walters (Universite de Geneve (CH))

I will present a nonperturbative recipe for directly computing the S-matrix in strongly-coupled QFTs. The method makes use of spectral data obtained in a Hamiltonian framework and can be applied to a wide range of theories, including potentially QCD. After discussing the general approach, I will demonstrate its application to the specific example of the 2+1d O(N) model at large N, using energy eigenstates computed with Hamiltonian truncation to reproduce the full 2-to-2 scattering amplitude for arbitrary (complex) center-of-mass energy. I will also discuss many avenues for future applications and generalizations

semiclassical gravity = statistical physics

• Jan de Boer (University of Amsterdam)

Complexity Coarse-Graining in Black Hole Information

• Netta Engelhardt (MIT)

Symmetries of TTbar-deformed CFTs and their holographic avatars

• Monica Guica (Paris Saclay)

I will discuss the classical and quantum symmetries of TTbar-deformed CFTs. These symmetries are infinite in number and, in a certain basis, organise into a Virasoro x Virasoro algebra with the same central charge as that of the undeformed CFT. I will present a quantum, abstract proof of the existence of these symmetries and three different - and fully explicit - classical perspectives: Hamiltonian, Lagrangian and holographic. Finally, I will show that the asymptotic symmetries of the three-dimensional asymptotically linear dilaton background in string theory, which is conjecturally dual to the "single-trace" TTbar deformation, take an identical form to those of TTbar-deformed CFTs, thus further strengthening this proposed connection.

Localizing information in quantum gravity

• Alexandre Belin

Locality is a powerful property of quantum field theory and implies that information can be strictly localized in regions of space, and is completely inaccessible from far away. On the other hand, the holographic nature of quantum gravity suggests that the theory is ultimately non-local and that information can never be localized deep inside some spacetime region, but rather is always accessible from the boundary. This is meant to hold as a non-perturbative statement and it remains to be understood whether quantum information can be localized within G_N perturbation theory. In this talk, I will address this problem from the point of view of the AdS/CFT correspondence. I will construct candidate local operators that can be used to localize information deep inside the bulk. They have the following two properties: they act just like standard HKLL operators to leading order at large N, but commute with the CFT Hamiltonian to all orders in 1/N. These operators can only be constructed in a particular class of states which have a large energy variance, for example coherent states corresponding to semi-classical geometries. The interpretation of these operators is that they are dressed with respect to a feature of the state, rather than to the boundary. The construction only works for sufficiently complicated states with large energ

Subalgebra-subregion duality: emergence of space and time in holography

• Hong Liu (MIT)

n holographic duality, a higher dimensional quantum gravity system emerges from a lower dimensional conformal field theory (CFT) with a large number of degrees of freedom. We propose a formulation of duality for a general causally complete bulk spacetime region, called subalgebra-subregion duality, which provides a framework to describe how geometric notions in the gravity system, such as spacetime subregions, different notions of times, and causal structure, emerge from the dual CFT. Subalgebra-subregion duality generalizes and brings new insights into subregion-subregion duality (or equivalently entanglement wedge reconstruction). It provides a mathematically precise definition of subregion-subregion duality and gives an independent definition of entanglement wedges without using entropy. Geometric properties of entanglement wedges, including those that play a crucial role in interpreting the bulk as a quantum error correcting code, can be understood from the duality as the geometrization of the additivity anomaly of certain algebras. Using general boundary subalgebras rather than those associated with geometric subregions makes it possible to find duals for general bulk spacetime regions, including those not touching the boundary. Applying subalgebra-subregion duality to a boundary state describing a single-sided black hole also provides a precise way to define mirror operators.

Partition function for a volume of space

• Manus Visser (DAMTP Cambridge)

We consider the quantum gravity partition function that counts the dimension of the Hilbert space of a spatial region with topology of a ball and fixed proper volume, and evaluate it in the leading order saddle point approximation. The result is the exponential of the Bekenstein-Hawking entropy associated with the area of the saddle ball boundary. This generalizes the classic Gibbons- Hawking computation which corresponds to the special case when the fixed volume is that of the static patch of de Sitter spacetime, and exhibits the holographic nature of nonperturbative quantum gravity in finite volumes of space.

Thermal correlators in AdS/CFT, ANECs and the Bootstrap

• Robin Karlsson (CERN)

The emergence of dynamical spacetime in the bulk in AdS/CFT, from metric fluctuations to black hole solutions, is an interesting challenge for the conformal bootstrap program. How are properties of the horizon and the singularity encoded in the CFT data? A set of minimal observables which plays an important role in this context are stress tensor correlators at finite temperature. I will discuss, from the bulk, how to calculate the thermal stress tensor two-point function and its decomposition in CFT data for multi-trace stress tensor operators. In the lightcone limit, the correlators are dominated by the ANEC and its higher spin generalizations. We further consider GB gravity in order to vary the stress tensor OPE coefficients and argue that when the ANEC is saturated, all the higher spin ANECs also are saturated. Moreover, the obtained data is consistent with ANEC interference effects. We end by discussing future directions such as universal features in the lightcone limit and how to probe deeper into the bulk using the bootstrap.

talk 10

• Herman Verlinde (Princeton University)

Black hole interiors and the emergence of time

• Lampros Lamprou (UBC)

Entropy functions for supersymmetric AdS Black Holes

• Jerome Gauntlett (Imperial College)

We consider supersymmetric $AdS_3\times Y_7$ solutions of type IIB and $AdS_2\times Y_9$ solutions of $D=11$ supergravity. These can arise as the near horizon limit of black strings in $AdS_5$ and and black holes in $AdS_4$ spacetimes, respectively. We explain how novel extremisation techniques enable one to compute physical observables without explicitly solving Einstein equations. This allows one to identify infinite new classes of AdS_3/d=2 SCFT pairs, as well obtain a microstate counting interpretation for infinite classes of supersymmetric black holes in AdS_4. A sub-class of examples correspond to branes wrapping certain two-dimensional orbifolds known as spindles and this has opened up a new direction in AdS/CFT with novel connections to accelerating black holes.

TBA

• Marco Meineri (Universite de Geneve (CH))

Narain-averaging the tensionless string

• Joshua Kames-King (EPFL)

I will describe work in progress w/ B.Knighton, A.Kanargias,M. Usatyuk on finding a stringy embedding of ensemble-averaging. Specifically we consider the recent duality between Narain T^c CFTs averaged over moduli space and exotic AdS_3 U(1)^c x U(1)^c gravity. We generalise this by performing the average over the symmetric product orbifold of T^c where the bulk dual now must include a discrete gauge group. By considering the case c=4 and the addition of susy we make contact to the duality of the tensionless string on AdS_3 x S^3 x T^4 and the symmetric orbifold orbifold of T^4.

New connections in celestial holography

• Andrea Puhm (Polytechnique)

Non-perturbative S-matrices from dispersive iterations

• Piotr Tourkine (CNRS, LAPTh, Annecy)

Black Holes in the Dual of Quantum Mechanics

• Rishi Mouland (DAMTP, University of Cambridge)

I will motivate and study a holographic duality between on one hand a theory of superconformal quantum mechanics, and on the other, M-theory on a particular background. I will exhibit a broad class of black hole solutions, whose entropy must be captured by a degeneracy of states in the quantum mechanics. Through an asymptotic study of the superconformal index in the supergravity regime, I will provide such a microstate counting for those black holes that are supersymmetric. I will finally speculate on the role of dualities of this form in understanding the basic building blocks of holography for higher-dimensional CFTs