String Theory Journal Club
2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2026-04-01 (Wednesday)
room 2.23, Pasteura 5 at 14:15 
Gaetan Borot (Humboldt University)Large N expansions for random partitions via Nekrasov equations
It is well-known that matrix models admit topological expansions as the size goes to infinity, that the asymptotic expansion to all-order can be determined from loop equations (Virasoro constraints) and take the form of Eynard-Orantin topological recursion. I will show how to a similar approach can be used (not only formally, but also rigorously) for random matrix models with discrete eigenvalues or models of random partitions. Loop equations are replaced by "non-perturbative Dyson-Schwinger equations" similar to those Nekrasov derived in 4d N = 2 supersymmetric gauge theories, there is a topological recursion but it is different from Eynard-Orantin one beyond the leading order. I will discuss application to random lozenge tilings on surfaces and the Kenyon-Okounkov conjecture (fluctuations are described by free bosonic field). Based on https://arxiv.org/abs/2601.16377 with Vadim Gorin and Alice Guionnet.
2026-03-24 (Tuesday)
room 2.22, Pasteura 5 at 12:15
Romuald Janik (Uniwersytet Jagieloński)The Ising model as a window on quantum gravity with matter
In this talk, I show that the Ising model CFT can be used to obtain some surprising insights into 3D (quantum) gravity with matter. I review arguments for the existence of its holographic description, and analyze the time dependence of perturbations of the theory at high temperature, which would correspond to throwing matter into a black hole in the dual gravitational picture. After an initial exponential damping - consistent with absorption by the black hole - the signal remarkably reemerges intact again, apparently at odds with the expected conventional black hole behaviour. Using the exact solvability of the Ising model CFT, I provide an explanation of this phenomenon in terms of the properties of bulk matter fields interacting with the BTZ black hole. This is made possible by the fact that the geometry/metric is not fundamental but a derived quantity in the Chern-Simons formulation of 3D gravity, which allows for evading a variant of the black hole information paradox in the present context. I argue that the observed mechanism should be generic in the AdS3/CFT2 context and should apply for any CFT2. I also briefly mention some work in progress.