During the semester we have a high energy seminar and a lunch seminar. In addition to these two seminars we participate in a joint theoretical high energy theory seminar in Newe Shalom. The joint seminar takes place on Tuesdays from 10:30 until 13:30 and includes two talks and lunch. This seminar is attended by the high energy groups of all the Israeli institutions and usually attracts a crowd of roughly twenty participants.
Title:Reggeized scattering, entanglement and chaos using AdS/CFT
ABSTRACT:The eikonalized parton-parton scattering amplitude at large energy and
large impact parameter, is dominated by the exchange of a hyperbolic surface in
walled AdS. Its analytical continuation yields a worldsheet instanton that is
at the origin of the Reggeization of the amplitude and a thermal-like
quantum entropy. I will construct the entangled density matrix following from the
exchanged surface, and show that its von-Neumann entanglement entropy
coincides with its thermal-like entropy. The ratio of the entanglement entropy
to the transverse growth of the exchanged surface is similar to the Bekenstein
entropy ratio for a black-hole, with a natural definition of saturation
and the on-set of chaos in high energy collisions. The largest eigenvalues
of the entangled density matrix obey a cascade equation in rapidity,
reminiscent of non-linear QCD evolution of wee-dipoles
at low-x and weak coupling. We suggest that the largest eigenvalues
describe the probability distributions of wee-quanta at low-x
and strong coupling that maybe measurable at present and future hadron-hadron
and lepton- hadron colliders.
Title: Landau diagrams in AdS and S-matrices from conformal correlators
Abstract: Quantum field theories in AdS generate conformalcorrelation functions on the boundary, and in the limit where AdS is nearly flat one should be able to extract an S-matrix from such correlators. We discuss a particularly simple position-space procedure to do so. It features a direct map from boundary positionsto (on-shell) momenta and thereby relates cross ratios to Mandelstam invariants. This recipe succeeds in several examples, includes the momentum-conserving delta functions, and can be shown to imply the two proposals based on Mellin space and on the OPE data.Interestingly the procedure does not always work: the Landau singularities of a Feynman diagram are shown to be part of larger regions, to be called `bad regions’, where the flat-space limit of the Witten diagram diverges. To capture these divergences we introducethe notion of Landau diagrams in AdS. As in flat space, these describe on-shell particles propagating over large distances in a complexified space, with a form of momentum conservation holding at each bulk vertex. As an application we recover the anomalousthreshold of the four-point triangle diagram at the boundary of a bad region.
Title: Boundary conditions for a free scalar field
In the first part of the talk, I will consider the problem of classifying the conformal boundary conditions (b.c.) for the free scalar CFT. We will see how to tackle this problem using conformal bootstrap techniques. In the case of 4d bulk, I will show ournumerical results, which feature a “kink” that indicates the existence of a non-trivial “interacting” b.c., besides the obvious Neumann and Dirichlet “free” b.c.’s.
In the second part of the talk, I will discuss the RG flow of a 4d free scalar field coupled to large N vector models on the boundary. The (classically marginal) coupling involves the boundary mode of the scalar and the O(N) single-trace scalar operator. Iwill explain that the resulting RG connects two fixed points with bulk and boundary decoupled, and the local 3d sector is the free vector model in one end, and the critical one in the other end. This same RG admits two weak-strong dual descriptions, one fromthe free end, and one from the critical end.
Abstract: We illustrate the appearance of quantum extremal islands in holographic setups in higher dimensions. We emphasize the close parallel with the behaviour of holographic entanglement entropy in more familiar settings.
Title : Multi-point Bootstrap (and the search for a single open/closed string description of N=4 SYM)
Title: The Unreasonable Effectiveness of Higher-Derivative Supergravity in AdS_4 Holography
Abstract: I will describe the four-derivative corrections to four-dimensional N=2 minimal gauged supergravity and show that they are controlled by two constants. Interestingly, the solutions of the equations of motion in the two-derivative theory are not modified by the higher-derivative corrections. I will use this to arrive at a general formula for the regularized on-shell action for any asymptotically locally AdS_4 solution of the theory and show how the higher-derivative corrections affect black hole thermodynamic quantities in a universal way. I will employ these results in the context of holography to derive new explicit results for the subleading corrections in the large N expansion of supersymmetric partition functions on various compact manifolds for a large class of three-dimensional SCFTs arising from M2- and M5-branes. I will also briefly discuss possible extensions and generalizations of these results.
Title: Fine probes of quantum chaos
Abstract: Quantum chaotic dynamics is associated to diverse physical phenomena and signatures. In this talk, we describe progress in building effective theories for three of these: the butterfly effect, the pole skipping phenomenon, and thermalization through the lens of entanglement entropy. We uncover their interplay by showing that the butterfly velocity plays an important role in all three manifestations of chaos. The discussion is informed by results from AdS/CFT and from models of SYK type.
Title: Gravity from Averaging CFTs
Abstract: I will explore the idea that certain theories of gravity in Anti-de
Sitter space are dual to an average over an ensemble of quantum
theories, rather than to a specific quantum theory. I will describe
an average over Narain’s family of two-dimensional conformal field
theories which describe free bosons on a torus, and compute the
partition function using the Siegel-Weil formula. The result takes
the form of a sum over geometries as one would expect in a theory of
gravity. But the gravitational theory looks more like a Chern-Simons
theory than like Einstein gravity.
Title: Global symmetry, Euclidean gravity, and the black hole information problem
Abstract: In this talk I will show how the essential ingredients of recent calculations of the Page curve of an evaporating black hole can be usedto generalize a recent argument against global symmetries beyond the AdS/CFT correspondence to more realistic theories of quantum gravity, illustrating a close connection between the absence of global symmetries and a unitary resolution of the black hole informationproblem. I’ll also give several low-dimensional examples of quantum gravity theories which do not have a unitary resolution of the black hole information problem, and which therefore can and do have global symmetries. Motivated by this discussion, I’ll conjecturethat in a certain sense Euclidean quantum gravity is equivalent to holography. Based on recent work with Edgar Shaghoulian.