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

Maciej Kolanowski (University of California Santa Barbara)

Multicritical matrix models made manageable

In recent years there has been a surge of interest in the matrix models in the context of 2d gravity. These models reproduce, via topological recursion, n-point functions of (super)JT gravity to all orders in perturbation theory in $G_N$ and thus are hoped to be windows into non-perturbative quantum gravity. Nevertheless, finding these matrix models explicitly is not an easy task. The methods used so far are getting computationally more involved as one increases the number of supersymmetries. Moreover, their success depends on an infinite number of seemingly accidental cancellations. We propose a new scheme of mapping supergravities into matrix models that is much simpler and makes all these cancellations explicit. As a corollary, we show that the spectrum of such matrix models is very rigid. In particular, the BPS part of their spectrum is uniquely determined by the non-BPS part. Joint work with Clifford Johnson.

room 2.25, Pasteura 5 at 12:15

Kanhu Kishore Nanda (Tata Insititute of Fundamental Research)

Aspects of dS/CFT holography

It has been suggested that a $dS_{d+1}$ spacetime of radius $R_{ds}$ has a holographic dual, living at future space-like infinity ${\mathcal I}^+$, with the bulk wave function being dual to the partition function of the boundary theory, [arXiv:astro-ph/0210603v5]. We consider some aspects of this correspondence. For underdamped scalars with mass $M^2R_{ds}^2>{d^2\over4}$, belonging to the principal series, we show that for the Bunch Davies vacuum, a suitable source in the boundary theory can be identified in terms of the coherent state representation of the wave function. We argue that terms in the resulting correlation functions, which are independent of the late time cut-off, satisfy the Ward identities of a conformal field theory. We also discuss other ways to identify sources, both in the under-damped and the over-damped case, where $M^2R_{ds}^2. Based on: https://arxiv.org/pdf/2407.02417

room 2.25, Pasteura 5 at 12:15

Pedram Karimi (IFT UW)

An Introduction to Dunkl operators and symmetric polynomials

Dunkl operators are a certain difference-differential operators defined on root systems. I will show that the action of Dunkl laplacian is closely related to Colagero-Sutherland hamiltonian, which has Jack polynomials as eigenfunction. Additionally, I will review the proof of Goulden and Jackson conjecture by Okounkov and address two of the three questions Okounkov raised in his paper.

room 2.25, Pasteura 5 at 12:15

Jacek Kenig (IFT UW)

Introduction to Batalin-Vilkovisky formalism

In this talk, I will introduce the Batalin-Vilkovisky (BV) formalism, a framework that utilizes homological algebra to construct and study gauge theories. I will begin by discussing the motivation for developing the BV formalism, highlighting the challenges it addresses in quantizing gauge theories. Following this, I will cover the necessary mathematical background and BV formalism itself. Finally, I will conclude the presentation with a practical working example to illustrate the formalism's application.

room 5.42, Pasteura 5 at 10:15

Maciej Kolanowski (University of California Santa Barbara)

Where do Schwarzian modes live? (Part II)

We calculate one-loop corrections to the nearly extremal black hole thermodynamics directly in the bulk. In this way, we confirm previous near-horizon calculations of the one-loop determinant. In particular, we find a family of modes that become zero modes in the extremal limit. In that limit, they localize at a finite distance from the horizon. Thus, we may interpret them as bulk counterparts of the Schwarzian modes that arise in the near-horizon geometry due to the SL(2,R) symmetry. Along the way, we explain certain confusions regarding the count of rotational zero modes (that contribute to the log corrections to the entropy).

room 2.25, Pasteura 5 at 12:15

Stanisław Kalinowski (IFT UW)

Field theories and exotic matter

Effective field theory is a great tool to study emergent and macroscopic behaviour in condensed matter physics. Especially exciting is their application to exotic states of matter, which are characterized by unusual properties such as spin-charge separation, charge fractionalization or immobile excitations. This often leads to interesting field theories. Examples include topological theories (Θ-term, Chern-Simons) and higher order gauge theories. The main goal of this talk is to present these fascinating phenomena and explain how they can be described by field theories.

room 2.25, Pasteura 5 at 12:15

Per Moosavi (Stockholm University)

Inhomogeneous conformal field theory out of equilibrium

Conformal field theory (CFT) in 1+1 dimensions is routinely used to effectively describe quantum many-body systems in equilibrium. Recently, CFT has been used to study such systems also out of equilibrium, and more recently, even in the presence of inhomogeneities varying on mesoscopic scales. Examples include quantum spin chains with spatially-varying couplings and trapped ultracold atoms. The resulting effective description is an inhomogeneous CFT where the propagation velocity is given by a position-dependent function, or equivalently, a CFT in curved spacetime. In this talk, I will present an exact analytical approach to such CFTs based on projective unitary representations of circle diffeomorphisms and properties of the Virasoro algebra. This approach can be used to study non-equilibrium scenarios, such as driven quantum systems, and generalizes previous results for a small subfamily of similar systems that involved only a finite-dimensional subalgebra to general inhomogeneities that require the full (infinite-dimensional) Virasoro algebra.

room 2.25, Pasteura 5 at 12:15

Rebekka Koch (University of Amsterdam)

Bound state production in the 1d interacting Bose gas

The last few years have witnessed a sustained deepening of the collaboration between experimentalists working on cold atom gases and theorists studying interacting many-body quantum systems in and out of equilibrium. On the theoretical side however, obtaining analytical results for strongly interacting quantum systems becomes almost impossible, with the exception of 1d Bethe ansatz solvable models. The Bose gas with contact interactions is one such example, that is moreover experimentally realizable. Interestingly, the Bose gas with attractive interactions is build from bound states but it is experimentally highly unstable in its equilibrium phase. Once pushed out of equilibrium, the Bose gas and its bound states are stabilized due to its underlying integrability structure. In this talk I will present our analytical results on the production of bound states through slow interaction changes from the repulsive to the attractive regime, using the recently developed framework of Generalized Hydrodynamics (GHD). The inherent difficulty to test our predictions by numerical benchmarks in the quantum realm has motivated us to study its semiclassical limit: we apply our ideas to the Non-Linear-Schrödinger equation, and we benchmark our analytical predictions against Monte Carlo simulations. Finally, our results are realized in a state-of-the-art experiment with cold Cesium atoms.

room 2.25, Pasteura 5 at 12:15

Dawid Maskalaniec (IFT UW)

Three Point Amplitudes in Matrix Theory

The BFSS model is a matrix model which is hypothetically dual to M-theory in 11-dimensional asymptotically flat space – it provides a concrete example of flat space holography. I will outline the computation of 3-point amplitude in the BFSS model given in 2312.12592. First, I will give an introduction to BFSS. Then, I will describe how one can compute the amplitude via a supersymmetric index calculation. Finally, I will briefly discuss how using this result, one can deduce the Lorentz symmetry of BFSS n-point amplitudes in the large N limit.

room 2.25, Pasteura 5 at 12:15

Miłosz Panfil (IFT UW)

Navier-Stokes equations for nearly integrable quantum gases

I will talk about our recent results with Maciej Łebek on “deriving” Navier-Stokes equations from microscopic dynamics of nearly integrable quantum models. Our approach connects the standard methods of the kinetic theory with recently developed generalized hydrodynamics. Besides formulating the Navier-Stokes equations, we find formulas for transport coefficients which take into account the integrable interactions non-perturbatively. As a result we find a non-zero viscosity, which in standard approaches is instead vanishing.

room 2.25, Pasteura 5 at 12:15

Emanuele Di Salvo (Utrecht University)

Relaxation Dynamics in Integrable Quantum Field Theories after a Quantum Quench

Out of equilibrium dynamics of integrable systems have been intensively studied in the past 20 years. However, a full characterisation of time evolution of an integrable field theory after a quantum quench is still missing. We investigate processes occurring during relaxation towards a steady state and describe them in terms of analytical properties of matrix elements of operators in the post-quench theory. All these results are fully general for integrable models and are checked against the predictions obtained from Ising field theory, transverse-field Ising lattice model, Sinh-Gordon and Sine-Gordon field theory.

room 2.25, Pasteura 5 at 12:15

Panagiota Adamopoulou (Heriot-Watt University, Edinburgh)

Set-theoretical solutions to the Yang-Baxter and entwining Yang-Baxter equations

I will present several examples of set-theoretical solutions to the Yang-Baxter and entwining Yang-Baxter equations. I will first describe how such (parametric) solutions to the Yang-Baxter equation, called Yang-Baxter maps, can be obtained from refactorisation problems of Darboux matrices associated to certain integrable PDEs of soliton theory. Then I will present a generalisation of such maps over Grassmann algebras and I will discuss some of their integrability properties (Lax representation, invariants) in this non-commutative setting.

room 2.25, Pasteura 5 at 12:15

Luigi Guerrini (IFT UW)

Fun with Supersymmetric Localization

Supersymmetric Quantum Field Theories are a distinguished class of theories where we can understand, test, and sometimes discover features that persist in the corresponding non-supersymmetric models. With that in mind, supersymmetric localization provides a powerful method to get exact results and thus probe physics beyond the perturbative regime. In this talk, I will review the technique in the context of 3d gauge theories and argue how their matrix model description emerges. Moreover, I will explain how turning on different background fields computes different QFT observables. I will focus on the supersymmetric Renyi entropy and integrated correlation functions of local operators and briefly discuss their holographic interpretations.

room 2.25, Pasteura 5 at 12:15

Daniel Bryan (IFT UW)

Black hole microstates, wall crossing and Seiberg-Witten theory

The counting of BPS black hole microstates has been an important development in string theory. Subsequently a degeneracy formula for 1/4-BPS dyons for 4d black holes has also been derived. This takes the form of an integral over the Weyl denominator of a Borcherds-Kac-Moody algebra. 1/4-BPS dyons can decay into pairs of electric and magnetic 1/2-BPS states at walls of marginal stability given by Weyl chamber boundaries associated to the algebra. We construct an analogous Lie algebraic counting function for 4d N=2 theories including Seiberg-Witten theory using subalgebras from the N=4 theory. This counting function also corresponds to the Weyl denominator of a Lie algebra and therefore encodes the walls and chambers in the theory including both BPS walls and walls of marginal stability. It subsequently counts the number of BPS states existing within each chamber.

room 5.42, Pasteura 5 at 12:15

Giuseppe Di Giulio (Universität Würzburg)

Entanglement in interacting Majorana chains and transitions of von Neumann algebras

Analytical insights into interacting quantum many-body systems are hard to come by. A particularly difficult aspect to study is the precise characterization of the phase diagram of a system based on its entanglement properties. Recently, a version of this problem has been tackled in the context of holography via a novel take on an old paradigm, namely the theory of von Neumann algebras. Different types of algebras are known to encode distinct entanglement properties, and identifying their occurrence provides new perspectives into the different phases of a system. In this talk, I introduce a model of Majorana fermions with two-site interactions consisting of a general function of the fermion bilinear. The models are exactly solvable in the limit of a large number of on-site fermions. In particular, I study a four-site chain, which exhibits a quantum phase transition controlled by the hopping parameters and manifests itself in a discontinuous entanglement entropy. Based on these results, I identify transitions between types of von Neumann operator algebras throughout the phase diagram. In the strongly interacting limit, this transition occurs in correspondence with the quantum phase transition. This study provides a novel application of the theory of von Neumann algebras in the context of quantum many-body systems.

room 5.42, Pasteura 5 at 12:15

Arindam Bhattacharjee (IFT UW)

Towards celestial holography in (2+1) dimensional pure gravity

Celestial holography is the idea that the holographic dual theory for an asymptotically flat spacetime is codimension 2 CFT living in the celestial sphere at null infinity. Originally proposed in 4 dimensions, this idea is non-trivial to extend in lower dimensional gravitational theories due to absence of propagating gravitons. In this talk, we will show the construction of a one-dimensional dual theory that effectively describes the phase space of (2+1) dimensional gravity near a Flat Space Cosmology saddle. This Schwarzian type dual theory, living on the celestial circle, describes the dynamics of (pseudo)-Goldstone modes associated with the asymptotic symmetries of flat space. We also compute the Bekenstein-Hawking entropy of Flat Space Cosmological solutions and find agreement with gravitational calculations.

room 5.42, Pasteura 5 at 12:15

Jędrzej Wardyn (IFT UW)

Density Matrix Renormalisation Group in a family of Tensor Network methods, part 2

In this talk, I will introduce Density Matrix Renormalization Group(DMRG) method in its original and Matrix Product State (Tensor train) versions using examples of 1D spin systems. DMRG, introduced by S. White in 1992, is a variational numerical method that was found to be particularly efficient for low-dimensional fermionic and spin systems. This method lets us look beyond Landau's theory into frustrated magnetic systems, quantum spin liquids and other exotic phases and phenomena of quantum matter. Since the conception of DMRG, many other methods have been created that fit into a family of Tensor Network(TN) methods. I would like to show how TN serves as a practical and elegant language to describe systems where topological and boundary effects play a crucial role via entanglement. I will provide a short overview of the current and emerging methods in this field.

room 5.42, Pasteura 5 at 12:15

Jędrzej Wardyn (IFT UW)

Density Matrix Renormalisation Group in a family of Tensor Network methods

room 5.42, Pasteura 5 at 12:15

Javier Magan (Instituto Balseiro, Centro Atómico Bariloche, Argentina)

ABJ anomaly as a U(1) symmetry and Noether's theorem

The Adler-Bell-Jackiw anomaly determines the violation of chiral symmetry when massless fermions are coupled to an abelian gauge field. In his seminal paper, Adler noticed that a modified chiral U(1) symmetry could still be defined, at the expense of being generated by a non-gauge-invariant conserved current. In this talk we show this internal U(1) symmetry transforms the Haag duality violating sectors (or non local operator classes), and explain how this provides a simple unifying perspective on the origin of anomaly quantization, anomaly matching, applicability of Goldstone theorem, and the absence of a Noether current. If time permits we will comment on recent literature where this symmetry is considered to be either absent or non-invertible.

room 5.42, Pasteura 5 at 12:15

Weronika Obcowska (MIMUW)

Skein modules

The purpose of the talk is to introduce of skein modules and explain their connections with the Jones polynomial. We will also explain their relationship to the Temperley-Lieb algebra. The seminar takes places in 5050 lecture hall in MIMUW department.

room 5.42, Pasteura 5 at 12:15

Jan Boruch (IFT UW)

Indices from the gravitational path integral: new forms of attraction

In recent years, the Euclidean gravitational path integral has proven to be a reliable tool for studying quantum mechanical aspects of black holes. An important quantity that can help us probe whether black holes behave like conventional quantum mechanical systems is the supersymmetric index computed directly from the gravitational path integral. In this talk, I will discuss the issue of multicentered black hole contributions to the Euclidean path integral that computes the supersymmetric index at finite temperature. In the context of Einstein-Maxwell theory in 4d, I will explain how the multicentered generalization of the Kerr-Newman black hole, called the Israel-Wilson solution, can be seen to satisfy the boundary conditions of the supersymmetric index and yields a regular contribution to the index. I will show how even though we perform the computations at finite temperature, the construction makes the value of the on-shell action depend only on the black hole charges, which can be viewed as a new form of the attractor mechanism. Finally, I will describe how we can extend the analysis to the most general solutions of N=2 4d supergravity, where the on-shell action becomes independent of the boundary values of the scalars. Based on recent work with Luca Iliesiu, Sameer Murthy and Joaquin Turiaci.

room 5.42, Pasteura 5 at 12:15

Wojtek Politarczyk (MIMUW)

Extended TQFT's – continuation

The purpose of the talk will be to answer students' questions concerning the previous talk of Jacek Kenig. If time permits, I would like to discuss topological aspects of TQFT's, i.e. classification of manifolds, etc. The seminar will take place in 5050 lecture room at MIMUW.

room 5.42, Pasteura 5 at 12:15

Jacek Kenig (IFT UW)

(Extended) functorial field theories

Functorial field theories, pioneered by Atiyah and Segal, are an attempt at axiomatizing certain aspects of quantum field theory. Unfortunately, their framework only takes into account non-local field theories. This defect can be fixed by considering extended functorial field theories, which are naturally expressed in the language of higher categories. After introducing basic definitions of functorial field theories, I will informally define a higher category of bordisms and give an intuition on how extended functorial field theories express locality of field theories.

room 5.42, Pasteura 5 at 12:15

Maciej Łebek (IFT UW)

The one-dimensional hard rod system

Classical gas of one-dimensional rigid spheres (1D Tonks gas) is one of the few examples of exactly solvable interacting many-body systems. The model is known for almost a century, but its properties are still extensively studied. Recently, the interest in the system was revived, because it constitutes the simplest non-trivial example of a model described within the Generalized Hydrodynamics (GHD) framework. The GHD theory describes large-scale behavior of generic classical and quantum integrable models in one dimension. I will review the most important static and dynamic features of the system and give a sketch of present research directions.

room 5.42, Pasteura 5 at 12:15

Bartek Lewandowski (MIMUW)

A short intro to knot theory

We will introduce basic concepts of knot theory and illustrate them with plenty of examples. The seminar will take place in lecture room 5050 in MIMUW department.

room 5.42, Pasteura 5 at 12:15

Weronika Obcowska (MIMUW)

A short intro to homology groups, part II

The purpose of the talk is to give a quick introduction to homology groups. Note: this seminar takes place in 5050 lecture room in MIMUW department.

room 5.42, Pasteura 5 at 12:15

Weronika Obcowska (MIMUW)

A short intro to homology groups

The purpose of the talk is to give a quick introduction to homology groups. Note: this seminar takes place in 5050 lecture room in MIMUW department.

room 5.42, Pasteura 5 at 12:30

Bowen Chen (IFT UW)

Geometry of the transport of modular Hamiltonians

In this seminar, I will briefly review some basics about modular theory and introduce the idea of modular parallel transport. Modular parallel transport solves the transport problem for a family of modular Hamiltonians, which can be state or region deformations. Though modular parallel transport can be defined for general theories, we pay special attention to holographic theories. In holography, modular parallel transport can be understood as certain diffeomorphism in the bulk. For other diffeos, it can be understood as modular paralle transport plus some amount of modular zero modes.