Talks

We consider linear superpositions of single particle excitations in a scalar field theory on AdS3 and evaluate their contribution to the bulk entanglement entropy across the Ryu-Takayanagi surface. We compare the entanglement entropy of these excitations obtained using the Faulkner-Lewkowycz-Maldacena formula to the entanglement entropy of linear superposition of global descendants of a conformal primary in a large c CFT obtained using the replica trick. We show that the closed from expressions for the entanglement entropy in the small interval expansion both in gravity and the CFT precisely agree. The agreement serves as a non-trivial check of the FLM formula for the quantum corrections to holographic entropy which also involves a contribution from the back reacted minimal area. Our checks includes an example in which the state is time dependent and spatially in-homogenous as well another example involving a coherent state with a Bañados geometry as its holographic dual.

The emergent geometry from large N matrix models is shown to be naturally granular, with a short distance cut-off proportional to 1/N. This is explicitly demonstrated for matrix quantum mechanics which is exactly mapped to a lattice boson with lattice spacing  1/N. In case of the double scaled c=1 matrix model, even though N is infinite, the exact boson theory has an effective short distance cutoff given by a scaled quantity proportional to the string coupling. This explains the finite entanglement entropy and finite S matrix elements of the 2D string theory in contrast with collective field theory where these quantities are divergent. We  also briefly discuss a lattice boson representation of time-dependent unitary matrix models.

In recent years, it has been realized that algebraic techniques can be used to compute formal entropy differences for semiclassical black holes in quantum gravity, and that these entropy differences are consistent with the Bekenstein-Hawking formula. I will explain how to remove the word "formal" from the previous sentence, by showing that the algebraic entropy differences have an interpretation in terms of microstate counting that is consistent with our usual ideas about statistical mechanics. Based on 2404.16098 with Akers.

What is the bulk Hilbert space of quantum gravity? In this paper, we resolve this problem in 2d JT gravity, both with and without matter, providing the first example of an explicit definition of a non-perturbative Hilbert space specified in terms of metric variables. The states are wavefunctions of the length and matter state, but with a non-trivial and highly degenerate inner product. We explicitly identify the null states, and discuss their importance for defining operators non-perturbatively. To highlight the power of the formalism we developed, we study the non-perturbative effects for two bulk linear operators that may serve as proxies for the experience of an observer falling into a two-sided black hole: one captures the length of an Einstein-Rosen bridge and the other captures the center-of-mass collision energy between two particles falling from opposite sides. We track the behavior of these operators up to times of order eSBH, at which point the wavefunction spreads to the com...

We will introduce (standard) future operator algebras. We show that standard future algebras transform covariantly under the action of an emergent (universal cover of) PSL(2,R). In the case of generalized free fields with spectral densities corresponding to AdS_2 and higher dimensional eternal black holes, this symmetry corresponds to, respectively, the bulk AdS_2 and the conformal symmetry on the horizon.

Humanity faces real and present problems. Our resources to address these problems are limited. It’s easy to think, then, that we should devote ourselves to our most promising solutions.

It’s easy, but it’s wrong.

The great paradox of scientific research is that pure exploration – research into deep questions motivated by pure curiosity, without concern for applications – is ultimately what transforms our lives in tangible, practical ways.

In this talk, I will speak not just as a physicist interested in puzzles of quantum entanglement and five-dimensional black holes, but as the director of an institute devoted to fundamental research. I make the case for blue-sky research, and for optimism about our shared future.

The entanglement negativity is a useful measure of quantum entanglement in bipartite mixed states. The holographic dual of this entanglement measure has been controversial with calculations based on CFT techniques conflicting with calculations in random tensor networks (RTNs) that predict replica symmetry breaking. In this talk, I will argue that replica symmetry is broken for general holographic states. The argument involves relating the entanglement negativity to the 1/2 Renyi entropy of a doubled state. In order to compute it holographically, I will also discuss a modified cosmic brane proposal for computing Renyi entropies for n

Recent work has produced a consistent picture of the holographic dual description of semi-classical gravity. I will describe this picture, several applications of this picture including the factorization puzzle and the information paradox, and some open questions.