Faculty of Physics University of Warsaw > Events > Seminars > String Theory Journal Club

String Theory Journal Club

2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025

room 2.25, Pasteura 5 at 12:15

Ignacy Nałęcz (IFT UW)

Scalar Field Condensation in the Early Universe

It is well known that the Universe underwent several phase transitions during its cooling. In this talk, I will discuss the possibility that one of the cosmological transitions was a violent first-order condensation of a scalar field, which could leave fingerprints such as a detectable stochastic gravitational-wave background. The formation of these relics hinges on dynamical processes: the nucleation and expansion of true-vacuum bubbles within the supercooled medium. I will show that incorporating an effective coupling between the plasma and the scalar field fixes the entropy production, which is necessary for analytically computing the fluid profiles that form around expanding bubble walls. This effective model of background–field–plasma interactions reveals that two stable shock-wave solutions can coexist; however, real-time hydrodynamic simulations indicate that the faster solution is preferentially realized. These results will affect the phenomenological study of first-order phase transitions in a large class of Standard Model extensions.

room 2.25, Pasteura 5 at 12:15

Stanisław Kalinowski (IFT UW)

1-form symmetries and their hydrodynamics

The main goal of this talk is to introduce the concept of 1-form symmetries and discuss the construction of the effective field theory of hydrodynamics with this type of symmetries. Furthermore, I will present the applications of this formalism to physical systems such as neutron stars, as well as possible extensions to other phenomena.

room 2.25, Pasteura 5 at 12:15

Maciej Dołęga (IMPAN)

b-deformed Hurwitz numbers, W-constraints, and refined topological recursion

Weighted Hurwitz numbers were introduced by Harnad and Guay-Paquet as objects covering a broad class of Hurwitz numbers of various types. A robust property of Hurwitz numbers is that they are governed by the celebrated topological recursion (TR) of Chekhov--Eynard--Orantin: a universal algorithm that allows computation of them recursively with respect to their topology. The program of understanding how TR can be used to compute different types of Hurwitz numbers was carried out over the last two decades by considering each case separately, and finally, the general case of rationally-weighted Hurwitz numbers was recently proved by Bychkov--Dunin-Barkowski--Kazarian--Shadrin. We will discuss a more general case of weighted $b$-Hurwitz numbers, which is a one-parameter deformation of Hurwitz numbers. We show that their generating function is annihilated by an explicit system of PDE that has an elegant combinatorial description and can be obtained from a representation of $W$-algebras. We also explain how to use this description to prove refined topological recursion for various interesting models. Our result gives a new explanation of the remarkable enumerative properties of Hurwitz numbers and extends it to the $b$-deformed case. This is joint work with Nitin Chidambaram and Kento Osuga based on 2401.12814 and 2412.17502.

room 2.25, Pasteura 5 at 12:15

Arindam Bhattacharjee (IFT UW)

Quantizing a Schwarzian theory and logarithmic corrections to entropy

In the previous talk, we discussed how a Schwarzian type theory appears as the 1D dual of 3D asymptotically flat spacetimes with pure gravity. In this part, we will derive the 1 loop partition function of the theory around classical saddles and use this to extract the logarithmic corrections to entropy of bulk cosmological solutions.

room 2.25, Pasteura 5 at 12:00

Maciej Nieszporski (KMMF UW)

Discrete integrable systems and set-theoretical Yang-Baxter equation

I will present some examples of nonlinear difference equations that admit a Darboux-Backlund transformationand then I will show how they are related to maps with Yang-Baxter property.

room 2.25, Pasteura 5 at 12:15

Arindam Bhattacharjee (IFT UW)

Logarithmic corrections to Entropy of flat cosmologies

It is well known that for Black holes and similar systems, the leading order entropy is proportional to area. The first correction to this is a log area term whose coefficient depends only on the infrared physics of the theory. In this talk, I will discuss how these log area terms can be calculated for three dimensional flat spacetimes from a 1D Celestial dual theory. Interestingly, these corrections are not recovered from flat limits of AdS/CFT and hints at novel contributions to entropy in flat backgrounds.

room 2.25, Pasteura 5 at 12:15

Falk Hassler (Uniwersytet Wrocławski)

Strings, Membranes, and a Hidden Symmetry Algebra in Quantum Gravity

Geometry underpins gravity, while the quantum world is governed by algebras of observables. In string theory, (super)gravity and its quantum corrections emerge from specific vibration modes of relativistic strings, described by vertex operator algebras in two-dimensional conformal field theories. However, the precise map between these two is highly non-trivial and is only known explicitly to the first orders in a perturbative expansion. I will reveal a new, infinite-dimensional symmetry algebra that at least reproduces the leading two orders of quantum corrections. Remarkably, it has the potential to evade a no-go theorem that rules out competing approaches to uncover hidden symmetries in supergravity beyond second-order corrections. Given that many of the algebraic structures encountered here have a natural generalization from strings to membranes, this suggests a similar approach to analyzing quantum corrections in 11-dimensional supergravity - the low-energy limit of M-theory. Beyond fundamental insights, these results have broad applications, including the construction of new supergravity solutions, the analysis of their spectrum, the computation of renormalization group flows in two-dimensional σ-models, and the study of integrable strings. A generalization of Cartan geometry is found on the mathematical side.

room 2.25, Pasteura 5 at 17:00

Sridip Pal (Caltech)

The Conformal Bootstrap: Non-perturbative explorations of Quantum Systems

Conformal field theories (CFTs) are special landmarks in the space of Quantum field theories. They sit at the fixed points of renormalization group flow and describe the physics of systems at critical points. CFTs provide an exact definition of quantum gravity via the holographic principle. Remarkably, the high-energy spectrum of a CFT encodes the physics of black holes, revealing deep insights into quantum gravity.
A powerful non-perturbative approach to understanding CFTs is the conformal bootstrap, which exploits fundamental consistency principles—locality, unitarity, and crossing symmetry—to extract exact results. In this talk, I will demonstrate how the analytical conformal bootstrap yields rigorous universal results about key observables in CFTs, with striking applications to black hole physics and entanglement entropy in statistical mechanics.
Furthermore, I will unveil a novel and profound connection between hyperbolic geometry and the conformal bootstrap. Surprisingly, the same bootstrap techniques that constrain CFTs provide nearly optimal bounds on the spectrum of the Laplacian on compact hyperbolic manifolds—offering a fresh perspective on these spaces as toy models for quantum chaos. This unexpected link opens new avenues for understanding both quantum chaotic systems and the mathematics of hyperbolic manifolds, illustrating the power of modern theoretical physics to bridge seemingly distant domains.

Zoom: https://uw-edu-pl.zoom.us/j/99356019605?pwd=9imwam3ZNLBME7iJZDG0bJcmwvoE3S.1

room 2.25, Pasteura 5 at 12:15

Christopher Couzens (University of Oxford)

Localising Romans Supergravity

In this talk I will discuss how Equivariant Localization can be used to compute observables in supergravity without the need to solve the equations of motion. We will use 6d Romans supergravity as our test case and show that the on-shell action is completely determined in terms of topological data in terms of a master formula. Our work allows us to recover known results in the literature and to make predictions for hitherto unknown solutions and their field theory duals.

Zoom: https://uw-edu-pl.zoom.us/j/94824769708

room B4.58, Pasteura 5 at 12:15

Yorgo Pano (IFT UW)

Double soft theorems and symmetries

Studying the symmetries of asymptotically flat spacetimes is a very interesting problem which can be tackled from different perspectives, one of which are soft theorems. They are low-energy theorems of the scattering process in flat spacetimes and are equivalent to the Ward identities of asymptotic symmetries preserving the asymptotic structure at null infinity. In this talk I will give an overview of this relationship and discuss the w-algebra discovered by Stominger et al. in the soft sector of gravitational theories from the collinear limit of graviton amplitudes. Finally, I will comment on the antisymmetric double soft graviton theorems and talk about their implications for the w-algebra.

room B4.58, Pasteura 5 at 12:15

Ariunzul Davgadorj (Politechnika Świętokrzyska)

Projective superspace techniques for gauge field theories

Projective superspace formalism is a manifestly supersymmetric approach to describe extended supersymmetric theories off-shell. In this method standard superspace coordinates are appended by a bosonic auxiliary CP^1=S^2 (where the R-symmetry group acts) factor and the superfields depend on this variable meromorphically, (infinite set of components). SU(2)_R symmetry transformations realized as coordinate transformations on this CP^1. I will introduce this formalism for the case of standard 4-dimensional N=2 supersymmetric Yang-Mills theory and then discuss a specific technique of separating the prepotential gauge field into parts that depend on this CP^1 factor and a part that does not. This technique leads to compact expressions for Lagrangians of given theories and also makes it straightforward to reduce higher supersymmetry into lower susy components.

room B4.58, Pasteura 5 at 12:15

Noemie Combe (MIMUW)

Quantum Cohomology, Feynman path integrals and more

In this quantum approach of Kontsevich, the intersection theory was generalized by Quantum Cohomology. The study by Kontsevitch was strictly related to the Feynman path integrals. We consider the Feynman path integrals in real and complex cases and give some generalization for general exponential families. Then we show that we are able to generalize some Feynman vacuum diagrams for Frobenius manifolds. These Frobenius manifolds are the cohomology vectors space of the target manifold, endowed with some differential geometric data.

room B4.58, Pasteura 5 at 12:15

Stephan Stieberger (Max Planck Institute, Munich)

Single-valued Integration, Double Copy and Superstring Amplitudes (in genus zero and one)

Open and closed superstring amplitudes at tree-level and one-loop have striking mathematical relations leading to the concept of single-valued integration and double copy in genus zero and one. Likewise at the physical side these properties lead to relations between gauge and gravitational amplitudes.

room B4.58, Pasteura 5 at 11:30

Karapet Mkrtchyan (Imperial College London)

Democratic Lagrangian formulation for arbitrary p-forms and electric-magnetic duality

We summarize the recent progress on the new democratic formulation of p-form dynamics, where p-forms and their dual (d-p-2)-forms are equal fundamental variables in d-dimensional spaces of Lorentzian signature. This formulation provides a simple Lorentz-invariant action for selfdual (chiral) p-forms in 2p+2 dimensions, with arbitrary abelian (self-)interactions. We provide a democratic formulation of non-linear electrodynamics (NED) in 3+1 dimensions, including arbitrary electric-magnetic duality-symmetric NED where both Lorentz and duality symmetry are manifest off-shell symmetries. We also illustrate a simple derivation for these actions from a topological theory in one higher dimension due to Arvanitakis et al and its generalization to arbitrary dimensions/forms. Applications of this method include democratic actions for type II 10d Supergravities and 11d Supergravity.

room B4.58, Pasteura 5 at 12:15

Zoran Ristivojevic (CNRS Université Paul Sabatier, Toulouse)

Exact result for the low-temperature free energy of one-dimensional bosons with contact repulsion

Conformal field theory predicts the leading-order temperature-correction in the free energy of one-dimensional critical systems. It scales with the second power of temperature with a universal prefactor. In the talk based on a recent preprint arXiv:2410.12986, the leading correction to this classic result will be derived in the case of integrable model of one-dimensional bosons with delta function repulsion. It scales with the fourth power of temperature. The corresponding prefactor will be calculated exactly for any repulsion strength.

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.

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.

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.

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.

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.

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.

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.