String Theory Journal Club
2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2024-11-19 (Tuesday)
room B4.58, Pasteura 5 at 12:15 
Tomasz Taylor (Northeastern University & IFT UW)de S-matrix
I will construct the S-matrix for the scattering of quantum particles in maximally symmetric (global) de Sitter spacetime.
2024-11-12 (Tuesday)
room B4.58, Pasteura 5 at 12:15
Fabian Ruehle (Northeastern University, USA)Learning knot invariance
Knots are embedded circles in a R^3 and are considered equivalent if related by ambient isotopy. We propose to use techniques from generative AI and contrastive learning to automate the process of learning knot invariance. We set up a neural network with a contrastive loss that clusters different representations from the same knot equivalence class in the embedding dimension. We also use transformers to map different representations from the same knot equivalence class to a single (arbitrary) representative of their class. We explain how to use the generative model to study the Jones unknotting conjecture and how we examine which invariants are learned by the trained model. Note: this talk will be online.
2024-11-05 (Tuesday)
room B4.58, Pasteura 5 at 12:15
Pavlos Kassotakis (KMMF UW)On quadrirational Yang-Baxter and pentagon maps
The Yang-Baxter and the pentagon equation serve as important equations in mathematical physics. They appear in two equally significant versions, the operator and the set-theoretical one. In this talk, we focus on the set-theoretic versions of both equations, where their solutions are known as Yang-Baxter maps and pentagon maps, respectively. First, we recall Yang-Baxter maps of a specific type (quadrirational maps) and show their connection to discrete integrable systems. Then, we propose a classification scheme for quadrirational solutions of the pentagon equation. That is, we give a full list of representatives of quadrirational maps on $\mathbb{CP}^1 \times \mathbb{CP}^1$ that satisfy the pentagon equation, modulo an equivalence relation. Finally, we demonstrate how Yang-Baxter maps can be derived from quadrirational pentagon maps.
2024-10-29 (Tuesday)
room B4.58, Pasteura 5 at 12:15
Takato Mori (Perimeter Institute)Horizon causality from holographic scattering in asymptotically dS3
I will discuss causality on a holographic screen in static patch (SP) holography of asymptotically de Sitter spacetimes. SP holography is one proposal of dS holography, however, its boundary description is mysterious due to the lack of concrete models in three or higher dimensions. Nevertheless, we can argue various properties including causality without relying on the detail of the theory by employing a theorem that holds generically in holography — the connected wedge theorem. It assures from quantum information that entanglement on the boundary when direct scattering in the bulk does not have a local boundary analog. We argue that based on the theorem, the causality on the holographic screen for SP holography should be induced from a point on null infinities (either future or past, depending on the sign of the momentum). This hints us toward a connection between two different dS holography proposals, SP holography and dS/CFT. This talk is based on my recent work with Victor Franken. The paper is available on arXiv: https://arxiv.org/abs/2410.09050.
2024-10-22 (Tuesday)
room 2.12, Pasteura 5 at 12:15
Michał P. Heller (Ghent University)Geometric interpretation of timelike entanglement entropy
Analytic continuations of holographic entanglement entropy in which the boundary subregion extends along a timelike direction have brought a promise of a novel, time-centric probe of the emergence of spacetime. We propose that the bulk carriers of this holographic timelike entanglement entropy are boundary-anchored extremal surfaces probing analytic continuation of holographic spacetimes into complex coordinates. This proposal not only provides a geometric interpretation of all the known cases obtained by direct analytic continuation of closed-form expressions of holographic entanglement entropy of a strip subregion but crucially also opens a window to study holographic timelike entanglement entropy in full generality. We initialize the investigation of complex extremal surfaces anchored on a timelike strip at the boundary of anti-de Sitter black branes. We find multiple complex extremal surfaces and discuss possible principles singling out the physical contribution. Based on 2408.15752 and work in progress.
2024-10-15 (Tuesday)
room 2.12, Pasteura 5 at 12:15
Souradeep Purkayastha (IFT UW)Quiver superconformal index asymptotics
The supersymmetric index of so-called quiver gauge theories (whose matter content can be expressed in terms of quivers) often admits an interesting large N factorization in terms of loops of the quiver. In this talk I discuss some techniques and results on the asymptotic degeneracy of the large N index for some such theories in 4d, and some recent developments on the so-called "giant graviton expansion" of the underlying U(N) matrix model.
2024-10-08 (Tuesday)
room 2.25, Pasteura 5 at 12:15
Luigi Guerrini (IFT UW)Wilson loops with an angle in N=2 theories
I will discuss a class of novel 1/4-BPS Wilson loops with a cusp in 4d N=2 gauge theories. Specifically, inspired by perturbative computations and results from localization, we conjecture a matrix model description for their expectation value. Building on this proposal, we examine their behavior in the strongly coupled 't Hooft limit of superconformal QCD and find a new phase transition regulated by the opening angle of the Wilson loop. Along the way, I will also explore physical connections to quantities such as bremsstrahlung and the cusp anomalous dimension.