11th Bologna Workshop on Conformal Field Theory and Integrable Models
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Deadline for registration: August 8, 2025 !!
!! Warning - Warning !!
There have been reports of phishing attempts by malicious actors posing as being connected to the workshop organization and offering unsolicited accommodation booking. If you receive communications from ops@gtravelservice.com, housing@gtravelhost.com or other similar "services", please be aware that these entities are in no way affiliated with our workshop. Please exercise caution and do not share any sensitive personal data with them!
-
-
08:20
Registration Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy -
Talks: Tuesday morning Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
09:00
Welcome
-
1
Preparing integrable eigenstates on a quantum computer
Recent advances have introduced deterministic quantum algorithms capable of preparing Bethe states, providing a unitary realization of the Bethe Ansatz. We systematize these developments by demonstrating that such circuits naturally arise from a well-established structure in quantum integrable models: the F-basis. We hope that this approach can help to characterize the computational complexity of preparing integrable eigenstates. In this sense, the Bethe circuits have proven to match the efficiency of previous state of the art algorithms for free fermions. In a related development, we demonstrate that eigenstates of a selected class of interacting spin chains can be prepared using polynomial resources in system size and particle number. We consider an integrable rigid-rod deformation of the spin 1/2 XXZ model with simple interactions that exhibits Hilbert space fragmentation. Realistic error-mitigated noisy simulations of the associated circuits with up to 13 qubits are performed, obtaining a promising relative error below 5%.
Speaker: Esperanza Lopez (Instituto de Fisica Teorica, UAM/CSIC) -
2
Quantum simulator preparation of W-States through many-body physics
W-states are quantum states possessing both bipartite and multipartite entanglement and are necessary for several relevant quantum algorithms. We propose a protocol to generate them with an arbitrary number of qubits on a Rydberg atoms platform, by exploiting ring (topological) frustration. To validate our state preparation, we develop a new Bayesian state tomography approach that leverage on accurate classical numerical simulations. In this way we prove high fidelities experimentally (up to 11 qubits) and numerically argue about promising scaling for tens of qubits. With this work, not only do we reach an unparalleled accuracy for the generation of these states compared to the existing approaches, but we also show once more how physics principles can overcome traditional barriers and be exploited toward quantum advantage.
Speaker: Prof. Fabio Franchini (Rudjer Boskovic Institute) -
3
Thermal form-factor expansion of the dynamical two-point functions of local operators in integrable quantum chains
We have initiated a study of dynamical two-point functions of arbitrary local operators in integrable lattice models by means of thermal form factor series. These are obtained as expansions in a basis of eigenstates of an appropriately defined quantum transfer matrix. The latter is different from the transfer matrix that generates the Hamiltonian. The quantum transfer matrix rather is an auxiliary object that generates lattice path integral representations of the partition function and of correlation functions of quantum chains. For integrable quantum chains it can be constructed in such a way that its spectrum and eigenstates can be calculated by integrable methods such as the algebraic Bethe Ansatz. After explaining the general formalism, I shall show that thermal form factor series provide explicit representations of dynamical two-point correlation functions of the XXZ quantum spin chain in the thermodynamic limit that are efficient for numerical and asymptotic analysis. Concrete examples of spectral functions and of current-current correlation functions that determine the transport properties of the spin chain will be considered.
References:
https://arxiv.org/abs/2311.17196
https://arxiv.org/abs/2307.13789
https://arxiv.org/abs/2202.05304
https://arxiv.org/abs/2012.07378
https://arxiv.org/abs/2011.12752Speaker: Frank Göhmann (Bergische Universität Wuppertal) -
10:50
Coffee break
-
4
D^2 models and black holes
After reviewing quantum integrable models with quantum group symmetry, we focus on the models associated with $D^{(2)}$. We first review the case $D^{(2)}_2$, whose continuum limit is a non-compact CFT that is related to a black hole sigma model. We finally turn to the general case $D^{(2)}_{n+1}$, and present preliminary results of joint work with Holger Frahm, Sascha Gehrmann and Ana Retore (to appear).
Speaker: Rafael Nepomechie (University of Miami)
-
09:00
-
Gong Session for Posters Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
5
Confinement of solitons in the double sine-Gordon model
The double sine-Gordon model is the non-integrable deformation of the standard sine-Gordon model caused by the cosine perturbation with the frequency reduced by the factor of 2. It was showed by Delfino and Mussardo [1], that this perturbation induces confinement of the sine-Gordon solitons, which become coupled into the ‘me- son’ bound states. I calculate [2] the meson masses in the weak confinement regime, which corresponds to the small deformation of the sine-Gordon model. It is shown in particular, that there is no qualitative difference between mesons and breathers in this regime: the sine-Gordon breathers slightly deformed by the perturbation term, smoothly transform into mesons upon increase of the sine-Gordon coupling constant.
References
[1] G. Delfino, and G. Mussardo, Nucl. Phys. B 516, 675 (1998).
[2] S. Rutkevich, SciPost Phys. 16, 042 (2024).Speaker: Sergei Rutkevich (Retired from Bergische Universität Wuppertal) -
6
Extracting 3D CFT Data from Thermal Correlators
I will describe how correlation functions of a conformal field theory placed on the thermal geometry $S^1 \times S^2$ can be used to obtain precise information about flat space CFT data, namely the spectrum and the OPE coefficients of primary operators. The focus will be primarily on thermal one-point functions. Although exact formulas for thermal one-point blocks are not known in this setting, I will explain how the Casimir equation they satisfy provides enough control to obtain series expansions of blocks in different regimes of their parameter space, as well as to derive an inversion formula that expresses OPE coefficients in terms of thermal one-point functions. These tools enable us to extract information about OPE coefficients across the entire spectrum of exchanged operators, combining exact data for low-lying operators with systematic asymptotic expansions in the heavy exchange regime. I will illustrate these results using the free theory as an example.
Based on 2506.21671
Speaker: Francesco Mangialardi (DESY) -
7
Graded S-matrices, fractional-spin charges and twisted TBAs
Integrable quantum field theories with $\mathbb{Z}_n$ symmetry arise from decomposing two-body scattering amplitudes into cyclically shifted components, leading to graded S-matrices that organize asymptotic states into internal $\mathbb{Z}_n$ sectors. This framework preserves a generalized notion of braiding unitarity and crossing symmetry, and features an infinite tower of conserved charges with fractional spin, setting the stage for fractional Smirnov-Zamolodchikov deformations. Graded TBA equations capture the finite-volume spectrum across twisted sectors: in the ultraviolet limit, preliminary analytical and numerical results are consistent with the spectrum of a cyclic orbifold $\mathrm{CFT}^{\otimes n} / \mathbb{Z}_n$. A structural connection with the ODE/IM correspondence also emerges.
Based on ongoing work with N. Brizio, N. Primi and R. Tateo.
Speaker: Tommaso Morone (Università di Torino) -
8
Multipoint correlation functions in the Sinh-Gordon 1+1d QFT
The S-matrix bootstrap program offers a unique possibility to compute explicitly the form factors of local operators in integrable quantum field theories. We shall build on those results so as to compute, in terms of explicit series of multiple integrals, the multipoint correlation functions in the Sinh-Gordon 1+1 dimensional quantum field theory, which is a simple case where the S-matrix is scalar and there is only one kind of particle. In particular, our expressions allow us to explicitly check the causalty principle on the level of the correlation functions. This is a joint work with K. Kozlowski.
Speaker: Alex Simon (ENS Lyon) -
12:10
Break
-
9
Circuit dynamics of free fermions in disguise
The models known as "free fermions in disguise" are a class of Hamiltonians with very peculiar properties: while they are directly solvable by any Jordan-Wigner (JW) transformation, they display a free-fermionic spectrum. Indeed, the mapping to free fermionic modes involves a complicated non-linear and highly non-local map. Because of this, contrary to standard JW-solvable spin chains, it is a non-trivial and partially open question to compute the dynamics in such models, or whether this can be done efficiently at all. In this talk, I will focus on a family of quantum circuits which are the discrete version of the dynamics of free fermions in disguise and present recent results pertaining to their time evolution. I will discuss the implications of our results for the classical simulability of this class of circuits, and the quantum simulation of "free-fermions in disguise" on a quantum computer.
Speaker: David Gyorgy Szasz-Schagrin (Dipartimento di Fisica e Astronomia, Universit`a di Bologna and INFN, Sezione di Bologna) -
10
Semiclassical form factors of composite branch-point twist operators in the sinh-Gordon model
The 1+1-dimensional sinh-Gordon model is a well-known example of a simple and well-studied integrable QFT with factorized scattering. We consider this theory on a multi-sheeted Riemann surface with a flat metric and branch points, which are represented by twist operators $\cal T_n$. Twist operators are interesting in the context of von Neumann and Renyi entanglement entropies in the original model on the plane.
The calculation of correlation functions on such surfaces is an important problem, typically carried out by spectral decomposition in terms of form factors of local operators, i.e. their matrix elements in the basis of stationary states. In integrable models a complete set of solutions to a system of bootstrap equations can be identified with the form factors of a unique operator; however, this identification in terms of the basic field remains problematic.
In this talk I aim to discuss the technique for finding form factors of special composite operators located at the branch points, as well as their descendants, in the semiclassical approximation.
Speaker: Amir Nesturov (University of Ljubljana) -
11
Quench dynamics of entanglement from crosscap states
The linear growth of entanglement after a quench from a state with short-range correlations is a universal feature of many body dynamics.
It has been shown to occur in integrable and chaotic systems undergoing either Hamiltonian, Floquet or circuit dynamics and has also been observed in experiments.
The entanglement dynamics emerging from long-range correlated states is far less studied, although no less viable using modern quantum simulation experiments.
In this talk, I will present the dynamics of the bipartite entanglement entropy and mutual information in quenches starting from crosscap states, a class of states constructed by entangling antipodal points of a finite and periodic system.
We consider the evolution of these initial states, in integrable and chaotic systems for both brickwork quantum circuits and Hamiltonian dynamics.
Specifically, I will show the different patterns of behaviors that we observe in dual unitary and random unitary quantum circuits, as well as free and interacting fermion Hamiltonians, which are explained by a modified membrane picture for the former case and a quasiparticle picture that can be derived explicitly for the latter.
For chaotic systems we have constant maximal entanglement entropy, whereas for integrable systems after an initial time delay we have a linear decrease followed by a series of revivals.
Mutual information is linearly decreasing from its initial maximal value in both cases, vanishing for chaotic, while exhibiting revivals for integrable systems.Speaker: Konstantinos Chalas (Istituto Nazionale di Fisica Nucleare) -
12
Sine-Gordon model at finite temperature: the method of random surfaces
The sine-Gordon theory is a paradigmatic integrable field theory, relevant for the description of many 1D gapped systems. Despite its integrability, calculating finite temperature physical quantities, such as correlation functions, remains a challenge. We generalize the numerical method of random surfaces to compute the free energy, and finite temperature one- and two-point correlation functions of exponential operators non-perturbatively. We demonstrate the method's accuracy by comparing our results to the predictions of other methods and to exact results in the thermodynamic limit, finding excellent agreement when the temperature is not too small with respect to the mass gap.
Speaker: Miklós Tóth
-
5
-
12:40
Lunch break Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy -
Posters: Tuesday Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
13
Extracting 3D CFT Data from Thermal Correlators
I will describe how correlation functions of a conformal field theory placed on the thermal geometry $S^1 \times S^2$ can be used to obtain precise information about flat space CFT data, namely the spectrum and the OPE coefficients of primary operators. The focus will be primarily on thermal one-point functions. Although exact formulas for thermal one-point blocks are not known in this setting, I will explain how the Casimir equation they satisfy provides enough control to obtain series expansions of blocks in different regimes of their parameter space, as well as to derive an inversion formula that expresses OPE coefficients in terms of thermal one-point functions. These tools enable us to extract information about OPE coefficients across the entire spectrum of exchanged operators, combining exact data for low-lying operators with systematic asymptotic expansions in the heavy exchange regime. I will illustrate these results using the free theory as an example.
Based on 2506.21671
Speaker: Francesco Mangialardi (DESY) -
14
Graded S-matrices, fractional-spin charges and twisted TBAs
Integrable quantum field theories with $\mathbb{Z}_n$ symmetry arise from decomposing two-body scattering amplitudes into cyclically shifted components, leading to graded S-matrices that organize asymptotic states into internal $\mathbb{Z}_n$ sectors. This framework preserves a generalized notion of braiding unitarity and crossing symmetry, and features an infinite tower of conserved charges with fractional spin, setting the stage for fractional Smirnov-Zamolodchikov deformations. Graded TBA equations capture the finite-volume spectrum across twisted sectors: in the ultraviolet limit, preliminary analytical and numerical results are consistent with the spectrum of a cyclic orbifold $\mathrm{CFT}^{\otimes n} / \mathbb{Z}_n$. A structural connection with the ODE/IM correspondence also emerges.
Based on ongoing work with N. Brizio, N. Primi and R. Tateo.
Speaker: Tommaso Morone (Università di Torino) -
15
Confinement of solitons in the double sine-Gordon model
The double sine-Gordon model is the non-integrable deformation of the standard sine-Gordon model caused by the cosine perturbation with the frequency reduced by the factor of 2. It was showed by Delfino and Mussardo [1], that this perturbation induces confinement of the sine-Gordon solitons, which become coupled into the ‘me- son’ bound states. I calculate [2] the meson masses in the weak confinement regime, which corresponds to the small deformation of the sine-Gordon model. It is shown in particular, that there is no qualitative difference between mesons and breathers in this regime: the sine-Gordon breathers slightly deformed by the perturbation term, smoothly transform into mesons upon increase of the sine-Gordon coupling constant.
References
[1] G. Delfino, and G. Mussardo, Nucl. Phys. B 516, 675 (1998).
[2] S. Rutkevich, SciPost Phys. 16, 042 (2024).Speaker: Sergei Rutkevich (Retired from Bergische Universität Wuppertal) -
16
Multipoint correlation functions in the Sinh-Gordon 1+1d QFT
The S-matrix bootstrap program offers a unique possibility to compute explicitly the form factors of local operators in integrable quantum field theories. We shall build on those results so as to compute, in terms of explicit series of multiple integrals, the multipoint correlation functions in the Sinh-Gordon 1+1 dimensional quantum field theory, which is a simple case where the S-matrix is scalar and there is only one kind of particle. In particular, our expressions allow us to explicitly check the causalty principle on the level of the correlation functions. This is a joint work with K. Kozlowski.
Speaker: Alex Simon (ENS Lyon)
-
13
-
Talks: Tuesday Afternoon Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
17
Coulomb branch integrability
The symmetry-broken phase of the N=4 super-Yang-Mills theory (SYM) is described by a D3-brane in the bulk of AdS. The D3-brane boundary conditions preserve integrability of the string, opening an avenue for applying boundary Bethe Ansatz to non-perturbative condensates (1pt functions) and possibly other observables on the Coulomb branch of SYM, which break conformal symmetry, generates a mass scale and has propagating massive particles.
Speaker: Konstantin Zarembo (Nordita) -
18
Spin glass criticality from conformal invariance
For half a century the critical points of spin glasses in two and three dimensions have been considered out of reach of analytical methods and have been studied numerically. We show how conformal invariance gives exact access to spin glass criticality in two dimensions.
Speaker: Gesualdo Delfino (SISSA and Istituto Nazionale di Fisica Nucleare) -
19
Algebraic Bethe Ansatz for models based on orthogonal algebras
We consider integrable models with $o_{2n+1}$ symmetry. Within the framework of Algebraic Bethe Ansatz,
we construct their Bethe vectors and rectangular recurrence relations.
These rectangular recurrence relations generalize the usual ones, and are new, even for models with gl(n) symmetry, which are obtained as a subcase.
We also compute the scalar products of Bethe vectors.Based on the papers arXiv:2412.05224 and arXiv:2503.01578
Speaker: Eric Ragoucy (LAPTh, CNRS) -
16:00
Coffe break
-
20
Large-scale fluctuations in the sine-Gordon field theory
We investigate large-scale fluctuations of conserved quantities and their associated currents in the sine-Gordon field theory. Our approach is based on the framework of Generalized Hydrodynamics, which has only recently become fully applicable across all regimes of the model. By combining this with Ballistic Fluctuation Theory, we analyse the distribution of conserved charges and the full counting statistics of currents. We derive analytical results in both the low- and high-temperature limits. Notably, we find that the cumulants of the topological charge distribution exhibit a fractal-like dependence on the coupling constant, mirroring the behaviour observed in the Drude weight of the topological charge.
Speaker: Márton Kormos (Budapest University of Technology and Economics; HUN-REN-BME-BCE Quantum Technology Research Group) -
21
Solvable lattice discretisation of sine-Liouville gravity: boundary observables
The sine-Liouville gravity, or the sine-Gordon model coupled to 2D gravity, is discretised as a dilute vertex model on random triangulations, which in turn has a dual description as a large N matrix model referred here as vertex matrix model (VMM). It is shown that in the scaling limit, the spectral curve of the vertex matrix model is analytically connected to the spectral curve of Matrix Quantum Mechanics (MQM), which is known to give a non-perturbative formulation of sine-Liouville gravity. The spectral curve has three critical points, one described by pure gravity and the other two described by $c=1$ gaussian matter fields compactified on circles with two different radii. The flow connecting the two $c=1$ critical points is the gravitational analogue of the massless flow in the imaginary coupled sine-Gordon theory. Unlike MQM, the spectral curve of the VMM has a neat interpretation in terms of boundary observables. The disk partition function and the bulk one-point function for fixed boundary length are not FZZT type and are expressed in terms of certain generalisation of the K-Bessel functions.
Speaker: Ivan Kostov (IPhT CEA-Saclay) -
22
The osp(2m|2n) QQ-system and the AdS₃ × S³ × S³ × S¹ Quantum Spectral Curve
The QQ-system plays a crucial role in the study of many integrable models, and it is the cornerstone of many techniques such as the Quantum Spectral Curve and the Separation of Variables. We will explore the structure of the QQ-system for the osp(4|2) super Lie algebra. Its key application will be the Quantum Spectral Curve for the study of string theory on AdS₃ × S³ × S³ × S¹ background with pure RR fluxes, which exhibits osp(4|2) x osp(4|2) symmetry when the radii of the two S³ factors are equal. From a comparison with the Asymptotic Bethe Ansatz and some inspiration from previous works, I will discuss a proposal for the analytical properties of the Q-functions in the osp(4|2) x osp(4|2) QQ-system that can be used to study this theory.
Speaker: Nicolò Primi (Istituto Nazionale di Fisica Nucleare) -
23
Painlevé equations, gauge theories and gravity
We study the linear problems in $z,t$ ($t$ the time) associated to the Painlev\'e III$_3$, III$_1$ and V and VI equations when the Painlevé solution $q(t)$ approaches a pole or a zero. In this limit the problem in $z$ for the Painlev\'e III$_3$ reduces to the modified Mathieu equation, that for the Painlevé III$_1$ to the Doubly Confluent Heun Equation and the ones for the Painlevé V and VI to the Confluent Heun Equation and to the Heun equation, respectively. These equations are Nekrasov-Shatashvili quantisations/deformations of Seiberg-Witten differentials for $SU(2)$ ${\cal N}=2$ super Yang-Mills gauge theory with number of multiplets $N_f=0,2,3,4$, respectively. On the gravity side, the Heun equation is the form to which (angular and radial) Teukolsky equations for Kerr
Newman-de Sitter geometries can be reduced, while the confluent Heun equation is the form of the Teukolsky equation for a Schwarzschild geometry.
In this talk I will discuss the problem of computing quantities - related to Heun equations - that can be relevant for both SUSY theories and classical gravity. From the technical point of view, one will benefit from techniques imported from quantum integrable models, in specific the 'kink method' of TBA.
This talk is based onD. Fioravanti, M. Rossi,
From Painlevé equations to ${\cal N}=2$ susy gauge theories: prolegomena,
arXiv: 2412.21148Speaker: Marco Rossi (Istituto Nazionale di Fisica Nucleare)
-
17
-
08:20
-
-
Talks: Wednesday morning Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
24
The quantum Mpemba effect
The Mpemba effect is a striking and counterintuitive phenomenon in which, under certain conditions, hotter water cools more quickly than colder water. Although originally observed in classical systems, recent theoretical and experimental studies have uncovered an analogous effect in extended quantum systems.
A specific manifestation of this quantum effect occurs when the system starts in a state that explicitly breaks a given symmetry, yet the time evolution leads to the eventual restoration of that symmetry, sometimes at an unexpectedly fast rate.To systematically investigate this phenomenon, we introduce the entanglement asymmetry, a quantity which quantifies the degree of symmetry breaking in a quantum state. This measure is inspired by concepts from entanglement theory in many-body systems and provides a powerful tool to track the restoration of symmetry over time. By leveraging entanglement asymmetry, we gain new insights into non-equilibrium quantum dynamics and the fundamental mechanisms governing symmetry restoration.
This talk will explore the theoretical foundations of the quantum Mpemba effect, recent experimental observations, and the implications of entanglement asymmetry for understanding non-equilibrium processes in quantum many-body physics.
Speaker: Prof. Pasquale Calabrese (Istituto Nazionale di Fisica Nucleare) -
25
Space-like asymptotics of the transverse two point functions of the XXZ chain at finite temperature
Finite temperature dynamical correlation functions of Yang-Baxter integrable quantum chains can be represented by thermal form-factor series. These are series in which every term is expressed in terms of the spectral data and the form factors of an appropriately defined dynamical quantum transfer matrix. We review the construction and exemplify its usefulness with the discussion of the leading term of the space-like asymptotic of the transverse correlation functions of the XXZ chain at finite temperature. This is a joint work with F. Göhmann
Speaker: Karol Kozlowski (CNRS,Laboratoire de Physique) -
26
Entanglement dynamics and Page curves in random permutation circuits
The characterization of ensembles of many-qubit random states and their realization via quantum circuits are crucial tasks in quantum-information theory. In this work, we study the ensembles generated by quantum circuits that randomly permute the computational basis, thus acting classically on the corresponding states. We focus on the averaged entanglement and present two main results. First, we derive generically tight upper bounds on the entanglement that can be generated by applying permutation circuits to arbitrary initial states. We show that the late-time
entanglement Page curves'' are bounded in terms of the initial state participation entropies and its overlap with themaximally antilocalized'' state. Second, comparing the averaged R\'enyi-$2$ entropies generated by $(i)$ an infinitely deep random circuit of two-qubit gates and $(ii)$ global random permutations, we show that the two quantities are different for finite $N$ but the corresponding Page curves coincide in the thermodynamic limit. We also discuss how these conclusions are modified by additional random phases or considering circuits of $k$-local gates with $k\geq 3$. Our results are exact and highlight the implications of classical features on entanglement generation in many-body systems.https://arxiv.org/pdf/2505.06158
Speaker: Michele Mazzoni -
10:30
Coffee break
-
27
Quantum and Classical Dynamics with Random Permutation Circuits
Understanding thermalisation in quantum many-body systems is among the most enduring problems in modern physics. A particularly interesting question concerns the role played by quantum mechanics in this process, i.e. whether thermalisation in quantum many-body systems is fundamentally different from that in classical many-body systems and, if so, which of its features are genuinely quantum. I will talk about a recent work, where we studied this question in minimally structured many-body systems which are only constrained to have local interactions, i.e. local random circuits. In particular we introduced a class of random permutation circuits, where the gates locally permute basis states modelling generic microscopic classical dynamics, and compared them to random unitary circuits, a standard toy model for generic quantum dynamics. Random permutation circuits permit the analytical computation of several key quantities such as out-of-time order correlators, or entanglement entropies. Remarkably, despite the fundamental differences between unitary and permutation dynamics, they exhibit qualitatively similar behaviours.
Speaker: Katja Klobas (University of Birmingham) -
28
Boundary quenches in the Lee-Yang model
We study local quenches induced by boundary changing operators in the scaling Lee-Yang model. At the critical point, we provide explicit results for how the matrix element of a bulk field evolves between pre- and post-quench vacuum states. The quench effect propagates within a light-cone, indicating a finite velocity for the spread of information. When a bulk perturbation is added, the model becomes massive; here we use integrability to develop a boundary form factor expansion for the same quantity. In both cases, a light-cone effect is present: the vacuum-to-vacuum amplitude transitions from its value before the quench to that after the quench. We validate the form factor expansion through a Hamiltonian truncation method.
Speaker: Máté Lencsés (Wigner RCP) -
29
Detect algebraic integrability of the (deformed) Rule 54 model
I will discuss the integrability property of a stochastic and quantum deformation of the Rule 54 cellular automaton: the simplest microscopic (deterministic) reversible model in 1+1 discrete space and time dimensions with strong local interactions. First, I will introduce the Rule 54 model and its two deformations:
1) In the stochastic case, I couple the system to stochastic boundary reservoirs and show that the resulting non-equilibrium steady states can be constructed explicitly in matrix product form.
2) In the quantum case, I explain how the model can be embedded into the Yang-Baxter integrability framework. It turns out that Yang-Baxter integrability is more common than previously thought!
Based on ongoing work with T. Prosen.Speaker: Chiara Paletta (Trinity College Dublin)
-
24
-
12:20
Lunch break Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy -
Posters: Wednesday Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
30
Circuit dynamics of free fermions in disguise
The models known as "free fermions in disguise" are a class of Hamiltonians with very peculiar properties: while they are directly solvable by any Jordan-Wigner (JW) transformation, they display a free-fermionic spectrum. Indeed, the mapping to free fermionic modes involves a complicated non-linear and highly non-local map. Because of this, contrary to standard JW-solvable spin chains, it is a non-trivial and partially open question to compute the dynamics in such models, or whether this can be done efficiently at all. In this talk, I will focus on a family of quantum circuits which are the discrete version of the dynamics of free fermions in disguise and present recent results pertaining to their time evolution. I will discuss the implications of our results for the classical simulability of this class of circuits, and the quantum simulation of "free-fermions in disguise" on a quantum computer.
Speaker: David Gyorgy Szasz-Schagrin (Dipartimento di Fisica e Astronomia, Universit`a di Bologna and INFN, Sezione di Bologna) -
31
Semiclassical form factors of composite branch-point twist operators in the sinh-Gordon model
The 1+1-dimensional sinh-Gordon model is a well-known example of a simple and well-studied integrable QFT with factorized scattering. We consider this theory on a multi-sheeted Riemann surface with a flat metric and branch points, which are represented by twist operators $\cal T_n$. Twist operators are interesting in the context of von Neumann and Renyi entanglement entropies in the original model on the plane.
The calculation of correlation functions on such surfaces is an important problem, typically carried out by spectral decomposition in terms of form factors of local operators, i.e. their matrix elements in the basis of stationary states. In integrable models a complete set of solutions to a system of bootstrap equations can be identified with the form factors of a unique operator; however, this identification in terms of the basic field remains problematic.
In this talk I aim to discuss the technique for finding form factors of special composite operators located at the branch points, as well as their descendants, in the semiclassical approximation.
Speaker: Amir Nesturov (University of Ljubljana) -
32
Quench dynamics of entanglement from crosscap states
The linear growth of entanglement after a quench from a state with short-range correlations is a universal feature of many body dynamics.
It has been shown to occur in integrable and chaotic systems undergoing either Hamiltonian, Floquet or circuit dynamics and has also been observed in experiments.
The entanglement dynamics emerging from long-range correlated states is far less studied, although no less viable using modern quantum simulation experiments.
In this talk, I will present the dynamics of the bipartite entanglement entropy and mutual information in quenches starting from crosscap states, a class of states constructed by entangling antipodal points of a finite and periodic system.
We consider the evolution of these initial states, in integrable and chaotic systems for both brickwork quantum circuits and Hamiltonian dynamics.
Specifically, I will show the different patterns of behaviors that we observe in dual unitary and random unitary quantum circuits, as well as free and interacting fermion Hamiltonians, which are explained by a modified membrane picture for the former case and a quasiparticle picture that can be derived explicitly for the latter.
For chaotic systems we have constant maximal entanglement entropy, whereas for integrable systems after an initial time delay we have a linear decrease followed by a series of revivals.
Mutual information is linearly decreasing from its initial maximal value in both cases, vanishing for chaotic, while exhibiting revivals for integrable systems.Speaker: Konstantinos Chalas (Istituto Nazionale di Fisica Nucleare) -
33
Sine-Gordon model at finite temperature: the method of random surfaces
The sine-Gordon theory is a paradigmatic integrable field theory, relevant for the description of many 1D gapped systems. Despite its integrability, calculating finite temperature physical quantities, such as correlation functions, remains a challenge. We generalize the numerical method of random surfaces to compute the free energy, and finite temperature one- and two-point correlation functions of exponential operators non-perturbatively. We demonstrate the method's accuracy by comparing our results to the predictions of other methods and to exact results in the thermodynamic limit, finding excellent agreement when the temperature is not too small with respect to the mass gap.
Speaker: Miklós Tóth
-
30
-
Talks: Wednesday afternoon Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
34
Boundary flows from a single round of measurements on gapless quantum states
Measurements can qualitatively alter correlations and entanglement emerging in gapless quantum matter. Using the Ising spin chain as case study, I will study the impact of measurements in an explicit protocol involving uncorrelated ancillae entangled with the critical chain and subsequently measured projectively. By varying the measurement basis, we induce renormalization‐group flows between distinct conformally invariant boundary conditions. I will also investigate the effects of measurements on the tricritical Ising model, uncovering how they can trigger a non-trivial flow to different boundary conditions. These results point to a new way of engineering and probing boundary criticality via local measurements.
Speaker: Ms Sara Murciano (CNRS) -
35
Eigenstate thermalization hypothesis: lessons from the minimal solvable model
Eigenstate thermalization hypothesis is a cornerstone of our modern understanding of thermalization and relaxation phenomena in quantum many-body systems. The studies mainly focus on chaotic dynamics, where there is solid numerical evidence supporting the standard ETH. The are however conflicting statements regarding its validity in integrable systems. By motivating and introducing a refined version of the ETH ansatz, I will discuss the structure and statistical properties of off-diagonal matrix elements in a simple integrable quantum field theory.
Speaker: ENEJ ILIEVSKI (University of Ljubljana) -
36
An integrable deformed Landau-Lifshitz model with particle production?
I will discuss the continuum limit of a non-Hermitian deformation of the Heisenberg XXX spin chain. This model has non-diagonalisable transfer matrix, and it appeared in the classification of 4x4 solutions of the Yang-Baxter equation. This model can also be obtained by a Drinfeld twist of the XXX spin chain and its continuum limit gives a non-unitary deformation of the Landau-Lifshitz theory. I will show that this deformed model still admits an infinite tower of conserved charges in involution, and they are generated recursively by a boost operator. Finally, I will show that this theory admits particle production 1$\to$2, where one of the outgoing particle is soft, and therefore compatible with the integrability of the theory. This talk is based on arXiv:2506.13598.
Speaker: Andrea Fontanella (Trinity College Dublin)
-
34
-
20:00
Social dinner Ristorante "Lambrusco & Tigelle"
Ristorante "Lambrusco & Tigelle"
Via Garavaglia 5/b, 40127 Bologna - Tel. +39 051514989
-
-
-
Talks: Thursday morning Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
37
Integrability and generalised symmetries
In this talk I will discuss recent advances of integrability related to generalised symmetries and fusion categories. In particular I will show a framework on how to introduce Lax operators and R-matrices in this context. I will discuss some new models and a relation with Temperley-Lieb algebras.
Speaker: Marius De Leeuw -
38
Constraints on RG flows between 2D CFT from generalized symmetries
In this talk I will present some recent advances on understanding RG flows between 2d CFT by employing non-invertible (generalized) symmetries.
After introducing the formalism of non-invertible symmetries, I will illustrate how the matching of their 't Hooft anomalies puts strong constraints on the RG group flow from perturbed UV fixed 2D CFT.
I will then focus on the specific case of Virasoro Minimal models, discussing the results of 2501.07511 with Stefano Negro.If time permits, I will also present some work in progress with Tomáš Procházka where we extend this formalism to study and predicts RG flows between minimal models of Corner Vertex Algebras, such that $W_N$ minimal models.
Speaker: Federico Ambrosino (DESY/Perimeter Institute) -
39
Non-local charges from perturbed defects
We investigate non-local charges for perturbations of two-dimensional conformal field theories that arise as perturbations of conformal defects. We find solutions for a wide range of perturbations including the well-known (1,2), (1,3) and (1,5) integrable perturbations of Virasoro minimal models (with associated local conserved charges), but we also find solutions for other bulk perturbations, such as (1,7), and we contrast this with the (non) existence of local conserved charges.
Speaker: Gerard Watts (King's College London) -
10:30
Coffee break
-
40
CFT tools for gravity: scattering, inspirals and ringdowns
We apply CFT and gauge theory inspired techniques to the study of gravitational scattering and collisions of binary systems in the extreme mass-ratio regime.
Speaker: Jose Francisco MORALES (Istituto Nazionale di Fisica Nucleare)
-
37
-
Gong Session for Posters Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
41
Entanglement and quench dynamics in the thermally perturbed tricritical fixed point
The Blume–Capel model, a spin chain system exhibiting a tricritical point described by a conformal field theory with central charge $c=7/10$, serves as a rich framework for studying its thermal perturbation, the $E_7$ integrable quantum field theory. In my work, I investigate both numerical and analytical aspects of the $E_7$ model, aiming to validate theoretical predictions and explore new phenomena relevant for experimental realization. The numerical component of the work utilizes the infinite Time Evolving Block Decimation (iTEBD) algorithm to simulate real-time dynamics, focusing on post-quench evolution. These simulations allowed identification of three out of four predicted even particles through spectral analysis. The analytical part centers on the form factor bootstrap program, through which I compute one- and two-particle form factors of the twist field form factors incorporating nontrivial symmetry structures. These results were validated using the $\Delta$-theorem. Further, I study the post-quench dynamics of the Blume–Capel model near the tricritical point, analyzing expectation values and entanglement entropies following $E_7$ mass quenches. The time evolution curves of local observables, the Neumann and the Rényi entropies exhibit strong agreement with theoretical predictions, thereby reinforcing the field-theoretical framework.
Speaker: Csilla Király (HUN-REN Wigner Reserch Centre of Physics) -
42
Long-time and large-distance asymptotics of the field-field correlation function of the impenetrable Bose gas in non-thermal equilibrium
The study of correlation functions of integrable models at their free fermion points often leads to representations in terms of Fredholm determinants (and their minors) of integrable integral operators. This occurs, for example, in dynamical two-point correlation functions of the impenetrable Bose gas, the XY and XX spin chains at finite temperature. In this talk, we address the problem of obtaining the long-time and large-distance asymptotics of Fredholm determinants of this type, using Riemann–Hilbert techniques. We present the asymptotic analysis in detail in a general setting and apply the resulting asymptotic expansion explicitly to the field–field correlation function of the impenetrable Bose gas in thermal and non-thermal equilibrium.
This talk is based on joint work with Frank Göhmann and Karol Kozlowski.
Speaker: Mikhail Minin (Bergische Universität Wuppertal) -
43
Nonanalytic correlation length in the Ising field theory
I present recent progress in computing finite-temperature dynamical correlation functions in the 1+1 dimensional Ising field theory, an integrable quantum field theory. Leveraging the fact that in the Ising model, the finite-temperature form factor expansion can be recast as a Fredholm determinant, I develop a numerical approach based on evaluating these determinants. This representation is especially powerful in the space-like regime, where only a few terms of the form factor series are sufficient to accurately compute the correlations. In contrast, the time-like regime requires an effective resummation of the entire series. I demonstrate that the Fredholm representation, combined with a suitable analytic continuation strategy, enables access to this regime as well, extending the reach of the method beyond previously tractable cases.
As a key application, I demonstrate that in the paramagnetic phase, the thermal correlation length displays an unexpected nonanalytic dependence on both the temperature and the space-time ray parameter. This effect persists even at the lattice level, as supported by new, yet unpublished results from the finite-temperature dynamics of the Ising spin chain. These findings suggest that the interplay between integrability and thermal dynamics gives rise to richer analytic structures than previously understood.
Speaker: István Csépányi -
44
Emergent Hydrodynamics in the Symmetric Dyson Exclusion Process
We study the \emph{symmetric Dyson exclusion process} (SDEP)---a lattice gas with exclusion and long-range, Coulomb–type interactions that emerge both as the maximal-activity limit of the symmetric exclusion process and as a discrete version of Dyson's Brownian motion on the unitary group. Exploiting an exact ground-state (Doob) transform, we map the stochastic generator of the SDEP onto the spin-$\tfrac12$ XX quantum chain, which in turn admits a free-fermion representation. This mapping yields closed, finite-size expressions for the time-dependent density and current in terms of modified lattice Bessel functions.
At macroscopic scales we conjecture that the SDEP displays \emph{ballistic}, non-local hydrodynamics governed by the continuity equation
$$ \partial_t \rho+\partial_x j[\rho]=0,\qquad j[\rho](x)=\sin\!\bigl(\pi\rho(x)\bigr)\,\sinh\!\bigl(\pi\mathcal{H}\rho(x)\bigr), $$
where (\mathcal{H}) is the periodic Hilbert transform, making the current a genuinely non-local functional of the density. This non-local one-field description is equivalent to a local two-field “complex Hopf’’ system and implies ballistic scaling (z=1).Closed evolution formulas allow us to solve the melting of single- and double-block initial states, producing limit shapes and arctic curves that agree with large-scale Monte-Carlo simulations. The model thus offers a tractable example of emergent non-local hydrodynamics driven by long-range interactions.
Speaker: Ali Zahra -
11:50
Break
-
45
Reduced fidelities for free fermions out of equilibrium
Quantum fidelities—like entanglement measures—originated in quantum information theory but have since become powerful probes of emergent phenomena in quantum many-body systems. In out-of-equilibrium settings, the most prominent example is the Loschmidt echo (LE), which quantifies the fidelity between an initial state and its time-evolved counterpart after a quantum quench. The LE is notably sensitive to dynamical quantum phase transitions.
However, accessing the full LE experimentally is challenging in extended systems, as it requires global knowledge of the quantum state. In this talk, I will introduce the reduced Loschmidt echo: a local version of the LE, computable from reduced density matrices. Focusing on free fermions out of equilibrium, I will present analytical results showing that the reduced LE retains key features of the full LE and admits a quasiparticle picture in the hydrodynamic limit.
I will also discuss the final-state fidelity, a complementary quantity designed to probe late-time dynamics and thermalization. Like the reduced LE, it supports a quasiparticle description, and offers a natural way to detect quantum Mpemba effects.Speaker: Gilles Parez (LAPTh, Université Savoie Mont Blanc, FR) -
46
QFT on Fuzzy AdS Spaces and Boundary Correlation Functions
As a contribution to understanding quantum spacetimes, we consider the quantum field theory of a massive scalar field on the Fuzzy AdS spacetime in two and three dimensions. We focus on boundary correlation functions, which, in the case of the commutative AdS bulk, are given by CFT correlators. In two dimensions, the fuzzy two-point function is calculated analytically and expressed in terms of the Appell F1 function, providing a two-parameter deformation of the conformal two-point function. In three dimensions, the result is given by a definite integral that is numerically calculated. We show how the obtained two-point function can be realized as a CFT three-point function of two local and one defect operator. Based on 2502.17595.
Speaker: Dusan Dordevic (Faculty of Physics, University of Belgrade) -
47
Matrix Models for Large N correlators in N=4 SYM
Three point-correlation functions of half-BPS operators in 𝒩=4 SYM are deceivingly complex observables. Non-renormalization theorems tell us that they can be exactly computed at the free point of the theory making them a perfect target for understanding non-perturbative gravitational effects in the large N expansion in regimes where the planar expansion is inadequate.
I will review techniques to efficiently compute such correlators in cases where the dimensions of the participating operators scale with powers of N. These methods allow us to systematically reproduce one-point functions of light single trace in general half-BPS backgrounds of type IIB supergravity. For the inverse reconstruction problem, I will explain how to build explicit operators dual to arbitrary LLM geometries. Then I will demonstrate how to extend these results to compute novel one-point functions of heavy probes in the large N limit via a D-instanton type formula. This gives sharp predictions for exact holographic vev's of giant graviton branes in LLM backgrounds. I will then present some results for correlation function of three heavy (Δ~N^2) operators.
I will finally comment on extensions of these techniques beyond the half-BPS sector, and the possible relation of the correlation functions of 1/4 and 1/8 BPS to lattice reductions of gauge theories.
Speaker: Adolfo Holguin (Trinity College Dublin)
-
41
-
12:20
Lunch break Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy -
Posters: Thursday Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
48
Entanglement and quench dynamics in the thermally perturbed tricritical fixed point
The Blume–Capel model, a spin chain system exhibiting a tricritical point described by a conformal field theory with central charge $c=7/10$, serves as a rich framework for studying its thermal perturbation, the $E_7$ integrable quantum field theory. In my work, I investigate both numerical and analytical aspects of the $E_7$ model, aiming to validate theoretical predictions and explore new phenomena relevant for experimental realization. The numerical component of the work utilizes the infinite Time Evolving Block Decimation (iTEBD) algorithm to simulate real-time dynamics, focusing on post-quench evolution. These simulations allowed identification of three out of four predicted even particles through spectral analysis. The analytical part centers on the form factor bootstrap program, through which I compute one- and two-particle form factors of the twist field form factors incorporating nontrivial symmetry structures. These results were validated using the $\Delta$-theorem. Further, I study the post-quench dynamics of the Blume–Capel model near the tricritical point, analyzing expectation values and entanglement entropies following $E_7$ mass quenches. The time evolution curves of local observables, the Neumann and the Rényi entropies exhibit strong agreement with theoretical predictions, thereby reinforcing the field-theoretical framework.
Speaker: Csilla Király (HUN-REN Wigner Reserch Centre of Physics) -
49
Long-time and large-distance asymptotics of the field-field correlation function of the impenetrable Bose gas in non-thermal equilibrium
The study of correlation functions of integrable models at their free fermion points often leads to representations in terms of Fredholm determinants (and their minors) of integrable integral operators. This occurs, for example, in dynamical two-point correlation functions of the impenetrable Bose gas, the XY and XX spin chains at finite temperature. In this talk, we address the problem of obtaining the long-time and large-distance asymptotics of Fredholm determinants of this type, using Riemann–Hilbert techniques. We present the asymptotic analysis in detail in a general setting and apply the resulting asymptotic expansion explicitly to the field–field correlation function of the impenetrable Bose gas in thermal and non-thermal equilibrium.
This talk is based on joint work with Frank Göhmann and Karol Kozlowski.
Speaker: Mikhail Minin (Bergische Universität Wuppertal) -
50
Matrix Models for Large N correlators in N=4 SYM
Three point-correlation functions of half-BPS operators in 𝒩=4 SYM are deceivingly complex observables. Non-renormalization theorems tell us that they can be exactly computed at the free point of the theory making them a perfect target for understanding non-perturbative gravitational effects in the large N expansion in regimes where the planar expansion is inadequate.
I will review techniques to efficiently compute such correlators in cases where the dimensions of the participating operators scale with powers of N. These methods allow us to systematically reproduce one-point functions of light single trace in general half-BPS backgrounds of type IIB supergravity. For the inverse reconstruction problem, I will explain how to build explicit operators dual to arbitrary LLM geometries. Then I will demonstrate how to extend these results to compute novel one-point functions of heavy probes in the large N limit via a D-instanton type formula. This gives sharp predictions for exact holographic vev's of giant graviton branes in LLM backgrounds. I will then present some results for correlation function of three heavy (Δ~N^2) operators.
I will finally comment on extensions of these techniques beyond the half-BPS sector, and the possible relation of the correlation functions of 1/4 and 1/8 BPS to lattice reductions of gauge theories.
Speaker: Adolfo Holguin (Trinity College Dublin)
-
48
-
Talks: Thursday afternoon Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
51
Free fermions in disguise: recent advances
Recently a family of quantum spin chains was discovered, which can be solved by hidden free fermionic structures. It was proven that these structures are not equivalent to the Jordan-Wigner transformation or any direct generalization thereof. In this talk we discuss recent results in this topic, including different families of such models, the computation of real time dynamics in them, and also the existence of quantum circuits with such free fermionic solutions.
Speaker: Balázs Pozsgai (Eötvös Loránd University) -
52
Applications of the Modified Algebraic Bethe Ansatz (MABA): Rectangular 6-Vertex Model with General Boundary Conditions (r6V-GBC) and Full Counting Statistics (FCS) for the XXX Twisted Spin Chain
We present recent applications of the Modified Algebraic Bethe Ansatz (MABA) to two-dimensional vertex models and one-dimensional spin chains.
First, we address the eigenvalue problem and scalar products within the MABA framework. In particular, we exploit the SL₂ invariance of the underlying R-matrix and introduce a modified representation theory that generalizes the conventional highest-weight formalism.
Next, we study the rectangular 6-vertex model with general boundary conditions (r6V-GBC), characterized by modified creation operators in the MABA and pseudo vectors from modified representation theory. We analyze both the homogeneous and thermodynamic limits, deriving boundary effects on the leading term of the free energy.
Finally, by applying the MABA to two distinct twists and using modified Slavnov scalar products, we obtain the Full Counting Statistics (FCS) for the XXX twisted spin chain.
This work was conducted in collaboration with R. Pimenta, N. Slavnov, B. Vallet, M. Cornillault and A. Hutsalyuk.
Speaker: Samuel Belliard (IDP Tours France) -
53
Tracy-Widom distribution in the six-vertex model
We consider the six-vertex model on the N x N lattice, with domain
wall boundary conditions, and at ice-point, $\Delta=1/2$. We focus on
the Emptiness Formation Probability (EFP), for which we build an
explicit and exact (although still conjectural) expression, as the
Fredholm determinant of some linear integral operator. We study the
asymptotic behaviour of the obtained representation at large N. In
particular, by tuning the geometric parameters of the EFP to the
vicinity of the arctic curve, we obtain the GUE Tracy-Widom
distribution. Joint work with Andrei Pronko. [Nucl. Phys. B 1004 (2024) 116565]Speaker: Filippo Colomo (Istituto Nazionale di Fisica Nucleare) -
16:00
Coffee break
-
54
ODE/IM correspondence and WN algebras
We want to discuss aspects of ODE/IM correspondence for WN algebras, with particular focus on the relevant symmetries of the family (in particular the triality symmetry) and the associated geometric structures.
We develop a systematic procedure for calculating the expressions for local higher spin charges in terms of solutions of Bethe ansatz equations of BLZ type (we write these equations explicitly for the case of W3 and W3 algebras). The key step is the application of WKB analysis to the operator associated via ODE/IM correspondence to each eigenstate of the commuting Hamiltonians.
The WKB curve is a branched covering curve of three-punctured sphere, which we identify with the mirror curve appearing in the related context of topological string (topological vertex). Due to high symmetries of the problem, all the calculations are reduced to this mirror curve.Speaker: Tomáš Procházka (Institute of Physics, Czech Academy of Sciences, Prague) -
55
Renormalized Angular Momentum Across Black Hole Perturbation Frameworks
The renormalized angular momentum appearing in the time-honored Mano–Suzuki–Takasugi (MST) method, which is useful for solving the confluent Heun equation as an infinite expansion of hypergeometric functions, is a fundamental quantity that arises in almost every black hole perturbation theory context, such as quasi-normal mode computations, tidal Love numbers, and waveforms. The appearance of this quantity is discussed both in the MST and in the Seiberg–Witten approaches, and some recent post-Minkowskian resummation properties in the eikonal regime are also examined.
Speaker: Giorgio Di Russo (Hangzhou Institute for Advanced Study) -
56
One-body correlations and momentum distributions of trapped 1D Bose gases at finite temperature
Since the early days of Bose-Einstein condensation in ultracold gas experiments the momentum distribution of the atoms has been a pivotal experimental observable. Measured via time-of-flight imaging, the momentum distribution has allowed to observe and characterize a wide range of phenomena in a wide range of systems. It also contributed to the development of theories describing out-of-equilibrium behaviour in 1D gases, such as being a key quantity in testing the accuracy of generalized hydrodynamics and various other important works.
In this talk we report on our recent results on introducing a general approximate method for calculating the one-body correlations and the momentum distributions of one-dimensional Bose gases at finite interaction strengths and temperatures trapped in smooth confining potentials. Our method combines asymptotic techniques for the long-distance behavior of the gas (similar to Luttinger liquid theory) with known short-distance expansions. We derive analytical results for the limiting cases of strong and weak interactions, and provide a general procedure for calculating one-body correlations at any interaction strength using a numerical method used to compute Green’s functions (needed as input to our theory). We benchmark our method against exact numerical calculations and compare its predictions to recent experimental results, finding good agreement.
Speaker: Attila Takács (Université de Lorraine) -
57
Fermionic Basis in Conformal Field Theory: The Free Fermion Point
In this talk, we discuss some aspects of the connection between the one-dimensional XXZ chain and two-dimensional conformal field theories. Namely, we consider the XXZ spin chain in the scaling limit in the Matsubara direction. Our approach is based on the fermionic basis construction developed in [1, 2, 3, 4]. The main feature of the fermionic basis is the factorization of the algebraic and physical parts of the model: the basis itself is constructed using the representation theory of the quantum group $U_q(\widehat{\mathfrak{sl}_2})$ and is independent of any physical data such as magnetic field, temperature, or boundary conditions. The physical properties of the model are encoded in two transcendental functions: $\rho(\zeta, \kappa)$ and $\omega(\zeta, \xi; \kappa, \kappa')$.
The main object of interest in any quantum field theory is the correlation function of local operators. The fermionic basis approach allows for a simple determinant description of all correlation functions, due to the so-called Jimbo-Miwa-Smirnov (JMS) theorem [3]. The partition function of fermionic generators can be calculated using the function $\omega(\zeta, \xi; \kappa, \kappa')$ mentioned above. A recursive procedure for computing the $\kappa$-asymptotics of this function in the case of identical boundary conditions $\kappa = \kappa'$ was established in [4]. It is based on a linear integral equation for the function $\omega(\zeta, \xi; \kappa, \kappa')$ and employs the standard Wiener-Hopf method. The main limitation of this approach is that the correlation functions of the integrals of motion vanish when the boundary conditions are identical. To incorporate the action of the integrals of motion, it is therefore necessary to consider the case $\kappa \neq \kappa'$ as well. Unfortunately, this presents significant technical challenges.
In this talk, we discuss an alternative description for the function $\omega^{\text{sc}}(\lambda, \mu; \kappa, \kappa', \alpha)$. Instead of working with the integral equation, we use the master function approach developed in [5]. In the free fermion case, we determine the explicit form of the master function and, using the scaling limit of its functional relation with $\omega(\zeta, \xi; \kappa, \kappa')$, we calculate it explicitly, incorporating the action of the integrals of motion.
Finally, we discuss possible ways of lifting the result outside of the free fermion point.
[1] Boos H., Jimbo M., Miwa T., Smirnov F., Takeyama Y., Hidden Grassmann structure in the XXZ model, Comm. Math. Phys. (2007)
[2] Boos H., Jimbo M., Miwa T., Smirnov F., Takeyama Y., Hidden Grassmann structure in the XXZ model. II. Creation operators,Comm. Math. Phys.(2009)
[3] Jimbo M., Miwa T., Smirnov F., Hidden Grassmann structure in the XXZ model. III. Introducing Matsubara direction, J. Phys. A: Math. Theor. (2009)
[4] Boos H., Jimbo M., Miwa T., Smirnov F., Hidden Grassmann structure in the XXZ model. IV. CFT limit, Comm. Math. Phys. (2010)
[5] Boos H., Göhmann F., Properties of linear integral equations related to the six-vertex model with disorder parameter II, J. Phys. A: Math. Theor. (2012)Speaker: Sergei Adler (Bergische Universität Wuppertal)
-
51
-
-
-
Talks: Friday morning Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
58
Conformal blocks for black hole scattering
I will revise recent developments in the calculation of conformal blocks and its relation to black hole perturbations, especially the calculation of quasinormal modes for generic black hole solutions. A number of conformal operators are related to the black hole in asymptotically flat and anti-de Sitter spacetimes, including primary and Whittaker operators. An alternative view in terms of isomonodromy will be outlined and the symplectic structure ensuing from the equivalence will be described. I will close by explaining how quasinormal modes generically feature properties associated to quantum open systems, such as decay and hysteresis.
Speaker: Bruno Carneiro da Cunha (Departamento de Física, Universidade Federal de Pernambuco, Brazil) -
59
Integrals of Motion and ODE/IM correspondence
We study the ODE/IM correspondence between two-dimensional Wg-type conformal field theories and the higher-order ordinary differential equations
(ODEs) obtained from the affine Toda field theories associated with g-type
affine Lie algebras. We calculate the period integrals of the WKB solution to the
ODE along the Pochhammer contour, where the WKB expansions correspond to
the classical conserved currents of the Drinfeld-Sokolov integrable hierarchies. We also compute the integrals of motion for W algebras on a cylinder. Their eigenvalues on the vacuum state are confirmed to agree with the period integrals. These results generalize the ODE/IM correspondence to
higher-order ODEs and can be used to predict higher-order integrals of motion. This talk is based on the paper arXiv:2408.12917 and the joint work with M. Zhu and W. Kono.Speaker: Katsushi Ito (Tokyo Institute of Technology) -
60
One-loop effective actions and thermodynamics of near- extremal Kerr black holes
In this talk, we present an analytic method for performing exact computations of one-loop effective actions in black hole backgrounds. The method is based on a generalization of the Gelfand-Yaglom formalism to second-order linear ordinary differential equations, where the resulting expressions are governed by the connection coefficients of equations belonging to the Heun class.
As an application, we focus on linear perturbations around Kerr black holes within the Teukolsky formalism, and we present results for the logarithmic corrections to the entropy for massless particles of spin $s=1,2$.Speaker: Paolo Arnaudo (University of Southampton) -
10:30
Coffee break
-
61
Integrable ½ BPS Nahm pole defects in N=4 SYM
I will give an overview of the integrability properties of ½ BPS Nahm pole defects in N=4 SYM paying special attention to the case of Gukov-Witten surface defects which have only very recently been studied in the integrability context. Furthermore, I will discuss how localization results for one-point functions in these set-ups imply an intriguing structure of perturbation theory that might help us getting new insight on
wrapping corrections.Speaker: Charlotte Kristjansen (Niels Bohr Institute) -
62
Unconventional Transport in a System with a Tower of Quantum Many-Body Scars
We discuss unconventional transport phenomena in a spin-1 model that supports a tower of quantum many-body scars. In quantum many-body systems, the late-time dynamics of local observables are typically governed by conserved operators with local densities, such as energy and magnetization. In the model under investigation, however, there is an additional dynamical symmetry restricted to the subspace of the Hilbert space spanned by the quantum many-body scars. That significantly slows the decay of autocorrelation functions of certain coherent states and is responsible for an unconventional form of transport. We show that excited states with energy close to that of the quantum many-body scars play a crucial role in sustaining the transport. Finally, we propose a generalized eigenstate thermalization hypothesis to describe specific properties of states with energy close to the scars.
This work is based on [arXiv:2502.10387], a joint project with Gianluca Morettini, Maurizio Fagotti and Leonardo Mazza.
Speaker: Luca Capizzi -
63
Variational Method in Quantum Field Theory
We developed a variational approach to study a two-dimensional non-integrable quantum field theories through the lenses of integrable ones. We focus on the φ4 Landau- Ginzburg theory and compare it with the integrable Sinh-Gordon. We employ exact Vacuum Expectation Values and Form Factors of local operators of the Sinh-Gordon model for getting the best variational estimates of several quantities of the φ4 theory, such as the ground state energy on a finite volume or the physical mass as function of the coupling constant. We also apply Hamiltonian truncation methods at finite volume, studying the volume dependence of the variational method. At finite volume, the ground state energy, the mass and the elastic scattering matrix are studied numerically in the small-coupling regime.
Speaker: Artur Hutsaliuk (Istituto Nazionale di Fisica Nucleare)
-
58
-
12:20
Lunch break Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy -
Posters: Friday Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
64
Nonanalytic correlation length in the Ising field theory
I present recent progress in computing finite-temperature dynamical correlation functions in the 1+1 dimensional Ising field theory, an integrable quantum field theory. Leveraging the fact that in the Ising model, the finite-temperature form factor expansion can be recast as a Fredholm determinant, I develop a numerical approach based on evaluating these determinants. This representation is especially powerful in the space-like regime, where only a few terms of the form factor series are sufficient to accurately compute the correlations. In contrast, the time-like regime requires an effective resummation of the entire series. I demonstrate that the Fredholm representation, combined with a suitable analytic continuation strategy, enables access to this regime as well, extending the reach of the method beyond previously tractable cases.
As a key application, I demonstrate that in the paramagnetic phase, the thermal correlation length displays an unexpected nonanalytic dependence on both the temperature and the space-time ray parameter. This effect persists even at the lattice level, as supported by new, yet unpublished results from the finite-temperature dynamics of the Ising spin chain. These findings suggest that the interplay between integrability and thermal dynamics gives rise to richer analytic structures than previously understood.
Speaker: István Csépányi -
65
QFT on Fuzzy AdS Spaces and Boundary Correlation Functions
As a contribution to understanding quantum spacetimes, we consider the quantum field theory of a massive scalar field on the Fuzzy AdS spacetime in two and three dimensions. We focus on boundary correlation functions, which, in the case of the commutative AdS bulk, are given by CFT correlators. In two dimensions, the fuzzy two-point function is calculated analytically and expressed in terms of the Appell F1 function, providing a two-parameter deformation of the conformal two-point function. In three dimensions, the result is given by a definite integral that is numerically calculated. We show how the obtained two-point function can be realized as a CFT three-point function of two local and one defect operator. Based on 2502.17595.
Speaker: Dusan Dordevic (Faculty of Physics, University of Belgrade) -
66
Emergent Hydrodynamics in the Symmetric Dyson Exclusion Process
We study the \emph{symmetric Dyson exclusion process} (SDEP)---a lattice gas with exclusion and long-range, Coulomb–type interactions that emerge both as the maximal-activity limit of the symmetric exclusion process and as a discrete version of Dyson's Brownian motion on the unitary group. Exploiting an exact ground-state (Doob) transform, we map the stochastic generator of the SDEP onto the spin-$\tfrac12$ XX quantum chain, which in turn admits a free-fermion representation. This mapping yields closed, finite-size expressions for the time-dependent density and current in terms of modified lattice Bessel functions.
At macroscopic scales we conjecture that the SDEP displays \emph{ballistic}, non-local hydrodynamics governed by the continuity equation
$$ \partial_t \rho+\partial_x j[\rho]=0,\qquad j[\rho](x)=\sin\!\bigl(\pi\rho(x)\bigr)\,\sinh\!\bigl(\pi\mathcal{H}\rho(x)\bigr), $$
where (\mathcal{H}) is the periodic Hilbert transform, making the current a genuinely non-local functional of the density. This non-local one-field description is equivalent to a local two-field “complex Hopf’’ system and implies ballistic scaling (z=1).Closed evolution formulas allow us to solve the melting of single- and double-block initial states, producing limit shapes and arctic curves that agree with large-scale Monte-Carlo simulations. The model thus offers a tractable example of emergent non-local hydrodynamics driven by long-range interactions.
Speaker: Ali Zahra -
67
Reduced fidelities for free fermions out of equilibrium
Quantum fidelities—like entanglement measures—originated in quantum information theory but have since become powerful probes of emergent phenomena in quantum many-body systems. In out-of-equilibrium settings, the most prominent example is the Loschmidt echo (LE), which quantifies the fidelity between an initial state and its time-evolved counterpart after a quantum quench. The LE is notably sensitive to dynamical quantum phase transitions.
However, accessing the full LE experimentally is challenging in extended systems, as it requires global knowledge of the quantum state. In this talk, I will introduce the reduced Loschmidt echo: a local version of the LE, computable from reduced density matrices. Focusing on free fermions out of equilibrium, I will present analytical results showing that the reduced LE retains key features of the full LE and admits a quasiparticle picture in the hydrodynamic limit.
I will also discuss the final-state fidelity, a complementary quantity designed to probe late-time dynamics and thermalization. Like the reduced LE, it supports a quasiparticle description, and offers a natural way to detect quantum Mpemba effects.Speaker: Gilles Parez (LAPTh, Université Savoie Mont Blanc, FR)
-
64
-
Talks: Friday afternoon Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy-
68
The Parisi-Sourlas uplift
Parisi-Sourlas (PS) supersymmetry is known to emerge in some models with random field type of disorder. When PS SUSY is present, the $d$-dimensional theory allows for a $d−2$-dimensional description. In this talk I focus on the reversed question and provide new indications that any given CFT$_{d−2}$ can be uplifted to a PS SUSY CFT$_d$. I show that any scalar four-point function of a CFT$_{d−2}$ is mapped to a set of 43 four-point functions of the uplifted CFT$_d$ which are related to each other by SUSY and satisfy all necessary bootstrap axioms. As a byproduct this will imply 43 non trivial relations between conformal blocks across dimensions. I then explain why all diagonal minimal models admit an uplift and show exact results for correlators and CFT data of the 4d uplift of the Ising model. Despite being strongly coupled 4d CFTs, the uplifted minimal models contain infinitely many conserved currents and are expected to be integrable. Finally I will mention how to generalize the uplift in the presence of conformal defects like boundaries and Wilson lines.
Speaker: Emilio Trevisani (CERN) -
69
Confinement and false vacuum decay on the Potts quantum spin chain
Confinement is a central concept in the theory of strong interactions, which leads to the absence of quarks (and gluons) from the spectrum of experimentally observed particles. The underlying mechanism is based on a linear potential, which can also be realised in condensed matter systems. A one-dimensional example with a great analogy to quantum chromodynamics is the mixed-field three-state Potts quantum spin chain in the ferromagnetic regime. Compared to the analogous setting for the Ising spin chain, the Potts model has a much richer phenomenology and non-equilibrium dynamics, which originates partly from baryonic excitations in the spectrum and partly from the various possible relative alignments of the initial magnetisation and the longitudinal field in a global quantum quench. In my presentation, I will discuss how we obtain the low-lying excitation spectrum by combining semi-classical approximation and exact diagonalisation, and how the results can be applied to explain the various dynamical behaviours we observe in numerical simulations. Besides recovering dynamical confinement, as well as Wannier-Stark localisation due to Bloch oscillations similar to the Ising chain, a novel feature is the presence of baryonic excitations in the quench spectroscopy. In addition, when the initial magnetisation and the longitudinal field are misaligned, both confinement and Bloch oscillations only result in partial localisation, with some correlations retaining an unsuppressed light-cone behaviour together with a corresponding growth of entanglement entropy.
Reference:
[1] O. Pomponio, A. Krasznai and G. Takács, “Confinement and false vacuum decay on the Potts quantum spin chain,” Scipost Phys. 18 (2025) 082Speaker: Anna Krasznai (Budapest University of Technology and Economics) -
70
Local Quenches from a Krylov Perspective
In the last few years, quantifying the complexity of quantum states has found applications in many fields, including quantum information and computing, quantum dynamics in many-body systems, and black hole physics. Among these measures, the spread complexity roughly quantifies the size of the space of states visited along quantum dynamics. It is obtained through Krylov space methods, which consist of projecting the evolution of a state onto one-dimensional dynamics. In this talk, I will discuss the evolution of the spread complexity after a local quantum quench in conformal field theories (CFT). Interestingly, this quantity depends on the central charge of the considered theory. I will also show that, to get rid of all the non-universal contributions in the leading time behaviour, it is convenient to study another Krylov space quantity, the K-entropy, an entropy measure defined for pure states without the need for a bipartition. These results support the usefulness of the Krylov space methods to study quantum dynamics.
Speaker: Giuseppe Di Giulio
-
68
-
15:45
End Aula Magna
Aula Magna
Dept. of Physics and Astronomy - University of Bologna
Via Irnerio 46 - 40126 Bologna, Italy
-