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String Theory Journal Club

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Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

Jacek Kenig (IFT UW)

Path integrals and functorial field theories

I’ll explain how the gluing law for path integrals leads to the functorial and extended viewpoint on field theories, and how the geometric cobordism hypothesis reframes this as a classification of fully local theories from point-level data. I’ll end with brief examples, including my own computation in one-dimension.

Zapraszamy do sali 2.23, ul. Pasteura 5 o godzinie 14:15

Nikita Nekrasov (Simons Center for Geometry and Physics, Stony Brook University)

Geometry of relativistic hydrodynamics, part II

We formulate the covariant hydrodynamics equations describing the relativisticfluid dynamics as the problem of intersection theory on some infinite dimensional symplectic manifold associated with spacetime. This point of view separates the structures related to the equation of state, the geometry of spacetime, and the structures related to the (differential) topology of spacetime. We point out a five dimensional origin of the formalism of Lichnerowicz and Carter (and of Euler's equations for compressible ideal fluid). Our formalism makes it easy to incorporate the chiral anomaly and Onsager quantization. We clarify the relation between the canonical and Landau-Lifschitz flows, the meaning of Kelvin's theorem. Finally, we discuss some connections to topological strings and to canonical approaches to quasiclassical quantization of gravity. Joint work with Paul Wiegmann.

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

Nikita Nekrasov (Simons Center for Geometry and Physics, Stony Brook University)

Geometry of relativistic hydrodynamics, part I

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

Abhigyan Saha (IFT UW)

Unit Invariant Singular Value Decomposition

We will discuss variants of the singular value decomposition that are invariant under diagonal rescalings (changes of units) in a chosen basis, and show how they lead to new, scale-invariant notions of entanglement. Using these unit-invariant singular values, we define entropy-like measures for reduced density matrices, transition matrices, and other (possibly non-Hermitian) operators. We will illustrate these constructions in biorthogonal quantum mechanics as well as with link complement states in Chern-Simons theory, where in the latter framework, connected sums and framings of knots act naturally as diagonal and unitary transformations, respectively. Finally, we will describe random-matrix aspects, including quarter-circle and stretched quarter-circle laws for the distributions of the new singular values in Ginibre and Wigner Gaussian ensembles.

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

Tommaso Pedroni (SISSA)

Blowing-up the edge: connection formulae and stability chart of the Lame equation

Connections between different areas of physics often provide new perspectives on difficult problems and suggest guiding principles for their solutions. In this work, we show how the correspondence between 4d N=2 supersymmetric gauge theories, 2d conformal field theories and quantum integrable systems can be used to study periodic spectral problems, with a particular focus on the Lame equation. After introducing the key ingredients, we use 2d CFT techniques to solve the connection problem of the Lam e equation in terms of semiclassical Virasoro blocks. We then analyze their analytic structure, showing how apparent poles turn into branch points through a partial resummation that combines the AGT correspondence – relating 2d conformal blocks to 4d Nekrasov partition functions – with a specific limit of the C^2 blow-up equa-tions satisfied by these functions. Finally, we apply these results to the study of the periodic spectral problems of the Lam ́e equation, highlighting the new insights gained from this perspective.

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

David Osten (University of Wrocław)

An integrable sector for the membrane

In contrast to string sigma models which are well-known to be (classically) integrable in certain backgrounds, most famously flat space or AdS(5) x S(5), the same is not true for the membrane sigma model. Reasons for this are the non-trivial gravity on the world-volume but also the rarity of three-dimensional integrable field theories in general. Here, I will present the novel observation that a certain decoupling limit of the membrane in certain backgrounds will lead to an integrable model, the Manakov-Zakharov-Ward model – a known three-dimensional, but non-relativistic, integrable field theory. As an example of a supergravity background in which this limit is possible I present the 11d uplift of the pure NS-NS AdS(3) x S(3) x T(4) background.

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:30

Dennis le Plat (Wigner Research Centre for Physics, Budapest)

Resurgence and trans-series in integrable models

Resurgence and trans-series techniques provide a powerful framework for understanding non-perturbative phenomena in quantum field theory and beyond. In the first part of this talk, I will present a complete trans-series solution for key observables in the Lieb-Liniger model, a prototypical integrable system in one dimension. The trans-series is explicitly constructed from a perturbative basis derived via ordinary differential equations and is shown to satisfy non-trivial consistency conditions. For the second part of the talk, I will introduce determinant observables, which appear in supersymmetric gauge theories. For these, we recently uncovered a strikingly simple non-perturbative structure, where all trans-series corrections share a universal form. These results highlight the trans-series structure in integrable QFTs and its relevance to related models.
Based on arXiv:2504.05932 and arXiv:2509.20302

Zapraszamy do sali 2.22, ul. Pasteura 5 o godzinie 12:15

Miłosz Panfil (IFT UW)

Quantum hard rods - a simple many-body integrable model

Classical gas of hard-rods has served for a long time as a simple and exactly solvable problem of statistical physics of interacting particles. The quantum version of the model hasn't attract much attention so far. In this talk I will review the exact solution of the quantum model by the Bethe ansatz and then show new results on the correlation functions.

Zapraszamy do sali B4.58, ul. Pasteura 5 o godzinie 12:15

Pedram Karimi (IFT UW)

Exactly solvable Schrödinger operators related to the hypergeometric equation

This talk is based on joint work with Jan Dereziński available on arXiv:2509.03235. In this study, we investigate $6+3$ classes of one-dimensional Schrödinger operators that are solvable in terms of the Gauss hypergeometric function, treated as closed operators. In the first part of the talk, I will motivate this work by reviewing the Laplacian on symmetric Riemannian spaces. Following that, I will briefly revisit key concepts from spectral theory and the theory of hypergeometric functions. Finally, I will present several theorems concerning the Green functions of these operators and discuss the transmutation (a “magical” transformation) identities that connect different families. The aim of the talk is to share some useful ideas and perspectives in a clear manner, with an emphasis on conveying the essential concepts rather than technical details.

Zapraszamy na spotkanie o godzinie 16:00

Yoon Seok Chae (UC Davis)

Knots, series invariant and supergroup Chern-Simons theory

Topological quantum field theory (TQFT) has been a fruitful source ofinteractions between physics and topology. A classical example is thethree dimensional Chern-Simons theory from the 1980's. It yieldstopological invariants of links and three manifolds. In case of thelatter invariant, it was shown more recently that the invariant admitsa decomposition into a series invariant, which is a partition functionof a 3-dimensional (supersymmetric) QFT. This series invariant waslater generalized to a series invariant of knots. This motivated anextension of the series invariant of 3-manifolds to Lie supergroups, whose underlying physical theory is the supergroup Chern-Simons theory. This result was recently generalized to knots. In this talk, we review the original series invariants and introducethe recent generalization, and explore its properties and examples.https://uw-edu-pl.zoom.us/j/96227261664?pwd=6XSohvXIkXoEalbPcswHlPh1kd2UG8.1

Zapraszamy do sali 2.25, ul. Pasteura 5 o godzinie 14:15

Michał P. Heller (Ghent University and Jagiellonian University)

Insights into the microscopics of holographic complexity

I will discuss what the correspondence between a ’t Hooft-like limit of the Sachdev-Ye-Kitaev model and gravity teaches us about the microscopic interpretation of holographic complexity. Based on 2412.17785 (PRL in print) and work in progress.