Seminar on Tuessday at 11 by Yixuan Li (Padova University)

Titre: Efficient impurity solvers from few-body structures

Abstract: Quantum impurity problems describe a small cluster of interacting degrees of freedom coupled to a macroscopic Gaussian bath. Despite hosting strong correlations –  most notably the Kondo screening cloud – these systems admit a compact representation of their ground state and out-of-equilibrium when cast in an optimized single-particle basis: only a handful of non-Gaussian degrees of freedom then carry the many-body complexity. In this talk, I will show how these emergent few-body structures drastically reduce the cost of representing the relevant many-body objects, and how this insight can be systematically exploited to build efficient algorithms for both equilibrium and non-equilibrium simulations, combining basis rotations with tensor network methods. I will further demonstrate that analogous structures arise naturally in the Heisenberg picture at the operator level, where the locality of target observables together with few-body structures can be leveraged to simplify classical simulations of quantum impurity problems even further.

Speaker: Antoine Rignon-Bret

Time: 14:00 pm, Feb 25th Wednesday  

Location: Salle de Conférence Louis Michel

Title:  The second law: from Lindblad equation to black holes

Abstract: In this talk, I will present how techniques from quantum information theory and quantum thermodynamics can be used to derive the second law of thermodynamics for quantum fields. I will begin with the case of a finite quantum system undergoing a Markovian evolution driven by an infinite bath, whose dynamics are governed by the Lindblad equation and whose thermodynamic properties are well understood. Building on this framework, I will show how a natural generalization allows us to extend these methods to the thermodynamics of quantum fields defined on causal horizons. Unlike finite quantum systems, quantum field theory admits many unitarily inequivalent Hilbert spaces, each constructed from a distinct choice of vacuum state. I will argue that these different vacua can be interpreted as corresponding to different reservoirs driving the dynamics. In particular, I will demonstrate how Wall’s proof of the generalized second law fits naturally within this framework, and how analogous thermodynamic laws describing black hole thermodynamics emerge for asymptotic observers. These laws correspond to different thermodynamic potentials associated with distinct vacuum states, such as the Boulware, Hartle–Hawking, and Unruh vacua.

Speaker: Michal P. Heller

Time: 14:00 pm, Feb 18th Wednesday  

Location: Salle Jean Lascoux

Title:  Quasinormal perspective on nonthermal fixed points

Abstract: I will present nonthermal fixed points as paradigmatic far from equilibrium weak coupling phenomena characterised by a self-similar evolution in time. I will then discuss what strong coupling perspective based on the quasinormal modes insights into holographic thermalization and hydrodynamics can teach us about nonthermal fixed points. Based on 2307.07545, 2502.01622 and 2504.18754.

Speaker: Mitchell Woolley

Time: 16:00 pm, Feb 2th Wednesday  

Location: Salle de Conférence Louis Michel

Title:  The W-algebra bootstrap of 6d (2,0) theories (Continued.....)

Abstract: We outline progress toward the superconformal bootstrap of the mixed correlator bootstrap of 6d (2,0) SCFTs. The first step was achieved in [2506.08094], where we used the conjectured cohomological reduction of 6d (2,0) SCFTs to W-algebras to extract an infinite set of protected mixed correlator CFT data. To that end, we explicitly construct the W_g algebras of 6d (2,0) theories of type g={A,D} and impose Jacobi identities on generator OPEs to fix CFT data. We uplift this data and the twisted correlators to 6d and show how our CFT data is organized along conformal Regge trajectories. As an application, we demonstrate the consistency of this information with protected higher derivative corrections in the M-theory holographic dual on AdS_7 x S^4/Z_o.

Speaker: André Pinheiro

Time: 14:00 pm, Jan 28th Wednesday  

Location: Salle de Conférence Louis Michel

Title:  Holographic fluids with higher-form symmetries

Abstract: Higher-form symmetries are ubiquitous in physics. In this talk, I focus on the case where they are continuous and encode the conservation of extended objects. Applications include elasticity, superfluidity and phases of electromagnetism. Using holography, we explore effective descriptions of systems with the simplest case of a single higher-form symmetry. For energies well below temperature, these descriptions admit a (potentially extended) hydrodynamic regime. We verify this explicitly by studying AlAdS black branes charged under higher-form potentials. In particular, we compute quasinormal modes, starting with the low-density limit. Then, we focus on the bulk dual of a viscoelastic system and analyse instabilities for different equilibrium states corresponding to isotropic crystalline phases.

Spaeker: Rodrigo Olea

Time: 14:30 pm, Jan 23th Friday  

Location: Salle de Conférence Louis Michel

Title: Holographic Weyl Anomaly and Kounterterms

Abstract: The addition of Kounterterms leads to a finite action for Einstein gravity for asymptotically AdS spaces with a conformally flat boundary. In that sense, it provides a partial renormalization scheme when compared to standard holographic techniques. However, Kounterterms method has the advantage that they can be written down in an arbitrary dimension. In this talk, we show how to extract holographic information on conformal anomalies from the variation of odd-dimensional Einstein-AdS plus Kounterterms.

Seminar on machine learning methods for transport in warm plasmas, by Mufei Luo (Oxford) : 7th April, 2026, 14h30, CPHT Salle Louis Michel

Title:"Resolution-Independent Machine Learning Heat Flux Closure for ICF(inertial confinement Fusion) Plasmas."

Abstract: The fluid/gravity correspondence, the duality between black hole dynamics in Anti-de Sitter space and hydrodynamics, may be used to geometrize turbulent flow. Our goal is to translate the long-standing problem of explaining anomalous scaling exponents of fluid velocity structure functions into a language of gravity. We study the fluid phase of conformal matter driven by a randomly fluctuating gravitational potential, numerically solving the evolution of a black hole in Anti-de Sitter space with a fluctuating, stochastic boundary metric. Subtleties regarding the fluid's compressibility in this set up are discussed. We observe a scaling behavior of the energy power spectrum that is consistent with compressible flow and compute the energy dissipation and the fluid velocity distribution. We identify observables in the dual gravity theory corresponding to higher moments of the averaged energy dissipation which help to map anomalous scaling exponents to covariant quantities defined on the dual horizon.

Time: 15:30 pm, Jan 14th Wednesday  

Location: Salle de Conférence Louis Michel

Martin Pico (Universidad Autonoma de Madrid)

Title: Classifying consistent truncations from Exceptional Generalised Geometry

Abstract: Consistent truncations have proven to be one of the main tools to study low-dimensional effective theories of string theories. In this talk, I will discuss how new U-duality covariant formulations of higher-dimensional supergravities, Exceptional Generalised Geometries (EGG) and Exceptional Field Theories (ExFT), can be used to classify the possible consistent truncations that can be obtained from such higher-dimensional supergravities.