spring2021

KCL Strings Journal Club Spring 2021

Included page "clone:kclstrings" does not exist (create it now) Spring 2021 Journal Club Here's a summary of all the activity of our Journal Club during the Spring 2021 term.

Summary

Other papers discussed… Supersymmetry anomalies and the Wess-Zumino Model in a supergravity background (Giorgos, Peter) Topological violation of global symmetries in quantum gravity (K. Yonekura) - Alejandro Tails of Instability and Decay: a Hydrodynamic Perspective (Castro-Alvaredo, De Fazio, Doyon, Ziółkowska) Anomalies from correlation functions in defect conformal field theory (Herzog, Shamir) Instability of complex CFTs with operators in the principal series (Benedetti) - Teresa Vacuum states from a resolution of the lightcone singularity (Georgios) Separation of Variables in AdS/CFT: Functional Approach for the Fishnet CFT (Andrea, Nikolay, Fedor) The 4d superconformal index near roots of unity and 3d Chern-Simons theory (Arash, Sameer) Violation of Unitarity in Gravitational Subregions (Wall) - Kevin 1/N expansion of circular Wilson loop in N=2 superconformal SU(N)×SU(N) quiver and BPS Wilson loop in N=2 superconformal SU(N) "orientifold" gauge theory and weak-strong coupling interpolation (Beccaria, Tseytlin) - Michelangelo Instanton Worldlines in Five-Dimensional Ω-Deformed Gauge Theory (Neil, Rishi, Paul) A Crossing-Symmetric OPE Inversion Formula (Mazac) - Andrea Mar 10: Luca Iliesu (Stanford University) Title: The statistical mechanics of near-extremal and near-BPS black holes Abstract: An important open question in black hole thermodynamics is about the existence of a "mass gap" between an extremal black hole and the lightest near-extremal state within a sector of fixed charge. In this talk, I will discuss how to reliably compute the partition function of 4d Reissner-Nordstrom near-extremal black holes at temperature scales comparable to the conjectured gap. I will show that the density of states at fixed charge does not exhibit a gap in the simplest gravitational non-supersymmetric theories; rather, at the expected gap energy scale, we see a continuum of states whose meaning we will extensively discuss. Finally, I will present a similar computation for nearly-BPS black holes in 4d N=2 supergravity. As opposed to their non-supersymmetric counterparts, such black holes do in fact exhibit a gap consistent with various string theory predictions. Mar 5: JC - Julian Sonner (Geneva U.) Mar 3: Triangle Seminar (Pedro Vieira and Gonzalo Torroba) Feb 26: Romain Ruzziconi (TU Wien) Title: Charge Algebra in Al(A)dS spacetimes, BMS symmetries and flat limit Abstract: In this talk, I will discuss some generic boundary conditions in asymptotically locally (A)dS spacetimes that yield some flux through the conformal boundary. After a holographic renormalization procedure to remove the divergences arising at the level of the symplectic structure, the asymptotic symmetries and the charge algebra associated with these leaky boundary conditions will be presented. We will see that the charge algebra generically involves a field-dependent 2-cocycle in odd spacetime dimensions. In particular, when the general framework is restricted to three-dimensional asymptotically AdS spacetimes with Dirichlet boundary conditions, I will show that the 2-cocycle consistently reduces to the Brown Henneaux central extension. Then I will provide a specific example of leaky boundary conditions that leads to BMS-like symmetries in presence of non-vanishing cosmological constant. In the flat limit, I will show that these symmetries and the associated phase space reduce to those of Generalized BMS in asymptotically flat spacetimes. Based on: https://arxiv.org/abs/2011.02002 and https://arxiv.org/abs/2004.10769. Feb 24: Julian Sonner (Geneva U.) Title: Causal symmetry breaking: from quantum chaos to wormholes Abstract: Quantum chaotic systems are often defined via the assertion that their spectral statistics coincides with, or is well approximated by, random matrix theory. In this talk I will explain how the universal content of random matrix theory emerges as the consequence of a simple symmetry-breaking principle and its associated Goldstone modes. This approach gives a natural way to identify wormhole-like correlations, even for individual theories, in particular in theories with gravity duals. I will also discuss how to extend the Goldstone effective-field-theory approach to study operator correlation functions, and explain the relation of the EFT of quantum chaos to the bulk physics of wormhole-like geometries. Feb 19: Papers discussion We discussed: An order-unity correction to Hawking radiation (E. Flanagan) - Kevin Superconformal index of low-rank gauge theories via the Bethe Ansatz (F. Benini and G. Rizi) - Arash Feb 17: Wei Li (ITP, CAS, Beijing) Title: Bootstrapping BPS algebras from colored crystals Abstract: I will explain a method of constructing BPS algebras for string theory on generic toric Calabi-Yau threefolds. The approach is a bootstrap method based on the 3D colored crystals that describe BPS states of the system. The resulting algebras are quiver Yangians Y(Q,W) that are associated with the quiver and the superpotential of the theory. Feb 12: Papers discussion We discussed: On the structure of non-planar strong coupling corrections to correlators of BPS Wilson loops and chiral primary operators (Matteo Beccaria, Arkady A. Tseytlin) - Michelangelo Scattering from production in 2d (P. Tourkine, A. Zhiboedov) - Andrea Feb 10: Thomas Fischbacher (Google Research) Title: Adventures in Machine Learning and Theoretical Physics Abstract: Machine Learning has opened many new doors in science across multiple disciplines. Starting from recent work by the speaker and collaborators on in-depth explorations into the vacuum structure of gauged maximal supergravities using Machine Learning Technology, notably Google's TensorFlow library, we subsequently take a broader perspective on what happens when Machine Learning meets Physics. Feb 5: Papers discussion We discussed : Reparametrization modes in 2d CFT and the effective theory of stress tensor exchanges (Kevin) Codimension-n Holography for the Cones (Miao) Feb 3: Triangle January 29: Arash Arabi Title: Superconformal indices and the AdS/CFT correspondence Abstract: Superconformal indices are examples of exact partition functions that count - with appropriate Boltzmann weights -supersymmetric states in superconformal field theories (SCFTs). We will discuss their role in bridging field theory and gravity in the AdS/CFT correspondence. In particular, we will discuss large-N transitions in superconformal indices of 4d SCFTs, between confined, partially-deconfined, and fully-deconfined phases. In their confined phase the field theory indices encode the spectrum of supersymmetric multi-particle states, as well as 'tHooft anomalies, of the dual AdS_5 supergravity theory. In their fully-deconfined phase they encode supersymmetric black holes in AdS_5. The bulk interpretation of the partially-deconfined phases is unknown. January 27: Shai Chester (Weizmann Ins.) Title: Derivation of AdS/CFT for Vector Models Abstract: We derive an explicit map between the singlet sector of the free and critical O(N) and U(N) vector models in any spacetime dimension above two and to all orders in 1/N, and a bulk higher spin theory in anti-de Sitter space in one higher dimension. For the boundary theory, we use the bilocal formalism of Jevicki et al to restrict to the singlet sector of the vector model. The bulk theory is defined from the boundary theory via our mapping and is a consistent quantum higher spin theory with a well defined action. Our mapping relates bilocal operators in the boundary theory to higher spin fields in the bulk, while single trace local operators in the boundary theory are related to boundary values of higher spin fields. January 20: Agnese Bissi (Uppsala U.) Title: Towards all loop supergravity amplitudes Abstract: In this talk I will discuss how to extract the most trascendental piece of the four graviton amplitude in type IIB supergravity on AdS_5 \times S_5 at any loop order, from the dual four point function in N=4 Super Yang Mills. I will describe how to construct this part of the correlator/amplitude and its significance. I will conclude with some open problems and future directions. January 15: Papers discussion We discussed: Notes on hyperloops in N=4 Chern-Simons-matter theories (Nadav et al) Open Fishchain in N=4 Supersymmetric Yang-Mills Theory (Kolya, Julius, Nicolo) Quantum Information Theory of the Gravitational Anomaly (Simeon Hellerman, Domenico Orlando, Masataka Watanabe)