Organisation des séminaires et calendrier

Sebastian Harris (DESY)

Abstract: AdS/CFT is a strong–weak duality: it allows the study of strongly coupled gauge theories through classical geometry, and highly stringy regimes of quantum gravity through perturbative gauge theory. This complementarity makes the correspondence powerful but also difficult to prove, since there is usually no regime in which both sides are simultaneously under computational control. AdS3 offers a remarkable exception to this. There exists an exactly solvable AdS3 string background dual to a free 2d gauge theory. In this context, AdS/CFT can be fully derived: It was shown that all closed string scattering amplitudes match precisely the local correlation functions of the dual gauge theory. The talk reviews this remarkable derivation and presents recent progress extending it to encompass branes and open strings, as well as the dual interfaces and their local excitations.

Overview : https://indico.cern.ch/event/1514154/overview

In this colloquium, I will explain that there is a hidden geometry that exists within the Standard Model of Particle Physics. This is due to the modern interpretation of the Standard Model as an Effective Field Theory. I will review this fundamental paradigm and will explain the deep connection between Effective Field Theories and Geometry. This geometric perspective provides key insights into the interpretation of beyond the Standard Model physics, and opens up new and exciting directions for future exploration.

There is a longstanding dream of realizing QCD (and other confining gauge theories) as a string theory. The complete worldsheet theory lacking, our best tool so far has been to use an EFT description around the solution of a long confining string (or flux tube). While powerful, this approach treats equally any theory of dynamical strings, completely forgetting the underlying gauge theory. In this talk, we will see how to go beyond this paradigm by inputting into the worldsheet one prominent feature of these gauge theories, namely asymptotic freedom. After a brief review of the current status, I will discuss a worldsheet observable that smoothly interpolates between the EFT regime and the one where asymptotic freedom kicks in. We will then explore what implications this has on the scattering data of Goldstone bosons moving on the string.

Abstract: Microcausality states that field operators commute at spacelike separations. While this property holds directly for Lorentz-invariant states, it becomes more subtle when Lorentz symmetry is spontaneously broken. In this talk, I analyze the operatorial commutator in interacting scalar field theories using the interaction picture formalism. For theories without derivative interactions, I show that microcausality is preserved, ensuring that the interacting commutator still vanishes outside the standard Minkowski light cone, regardless of the state considered. In contrast, derivative interactions modify the free-theory commutator by introducing corrections proportional to derivatives of delta functions, evaluated on the light cone of the free theory. When expectation values are taken, these corrections cancel in Lorentz-invariant states but persist in states where Lorentz symmetry is spontaneously broken. I show that these terms are the signal of a perturbative shift in the light-cone structure of the free theory, due to interactions. Finally, I discuss what goes wrong with the standard argument according to which Lorentz invariance implies microcausality.

Using necessary and sufficient conditions for the saturation of the Araki-Lieb (AL) and related  inequalities which are realized holographically in black hole geometries, we prove that a typical pure state in a large N holographic CFT has two associated length scales that are determined only by the energy and conserved charges; one of them is a microscopic length scale L_{UV}, and the other is an infrared length scale L_{H} > L_{UV}.  Furthermore, the degrees of freedom between these two length scales are effectively split into two factors, one purifying the degrees of freedom at length scales smaller than L_{UV} and the other purifying those at length scales larger than L_{H}. Remarkably, the pure state factor involving the ultraviolet degrees of freedom is state independent. We also find precisely how deviations from this architecture are exponentially suppressed by studying quantum mutual information of two non-overlapping regions. Our results imply that all black holes can be isolated from the asymptotic region by a well-defined hypersurface which is the envelope of all critical entanglement wedges for which AL is saturated, and the split property emerges in the region bounded by this hypersurface and the horizon.

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