Mercredi 5 Fevrier 2025, 10:30 à IHES, Amphithéâtre Léon Motchane ( Cours de l'IHES )	MATH-IHES (TBA)	math
Laure Saint-Raymond ( IHES )	Hard Sphere Dynamics in the Low Density Limit (3/4)
Abstract:	At the microscopic level, a gas is a collection of interacting neutral particles. The very large number of degrees of freedom and the sensitivity of the system to very small perturbations mean that it is essentially impossible to predict its dynamics deterministically. At the end of the 19th century, Boltzmann proposed describing the behaviour of gas in an alternative way, using a statistical approach. A natural question is whether the assumption of statistical independence that underlies this model is compatible with microscopic dynamics and in what sense the Boltzmann equation is a good approximation. This course will provide some answers to this question, within the simplified framework of contact interactions. 1. The Boltzmann equation, the chaos hypothesis and the H theorem 2. Law of large numbers for the dynamics of hard spheres 3. Correlations, dynamic clusters 4. Fluctuations and large deviations for the dynamics of hard spheres

Mercredi 5 Fevrier 2025, 11:00 à APC, 454A-Luc Valentin	APC-COLLOQUIUM (Colloquium de l'APC)	hep-th
Raffaele Tito D'agnolo	A New Chapter in the Quest for Dark Matter and its Connection to Gravitational Waves
Abstract:	Dark Matter was discovered more than 90 years ago through its gravitational effects. It makes up 80% of the matter in our Universe and about a quarter of its present energy density. We have spent decades trying to detect it in the laboratory, but to date its microscopic origin remains mysterious. The vast majority of our theoretical and experimental effort has been devoted to the exploration of relatively heavy dark matter candidates, with masses comparable to particles that we can produce at our highest energy colliders. In this talk I will review how in the last five to ten years a new perspective has emerged in particle theory, shifting our attention to ultralight dark matter candidates, in particularly the axion. This has generated a flurry of experimental activity, with a few pioneering efforts now setting up prototypes, and new ideas appearing almost weekly on the arXiv. I will review both the theoretical appeal of these dark matter candidates and the new ideas proposed to detect them experimentally. Furthermore, ultralight dark matter is well described in the laboratory as a coherent classical field. Its detection has interesting overlaps with that of high-frequency gravitational waves. I will show how thinking about ultralight dark matter was useful to establish a fundamental detection limit on gravitational waves. In practice it is not feasible to detect gravitational waves from primordial stochastic backgrounds at frequencies above those probed by existing interferometers.

Mercredi 5 Fevrier 2025, 12:45 à LPENS, 3 rue dUlm, College de France	FORUM-ENS (Forum de Physique Statistique @ ENS)	cond-mat.stat-mech
Nina Javerzat ( LIPhy )	Renyi complexity in mean-field disordered systems
Abstract:	Configurational entropy, or complexity, plays a critical role in characterizing disordered systems such as glasses. Yet its measurement often requires significant computational resources. Recently, Renyi entropy, a one-parameter generalization of the Shannon entropy, has gained attention across various fields of physics due to its simpler functional form, making it more practical for measurements. I will explain that the Renyi complexity corresponds, in disordered models, to a generalized Franz-Parisi potential, namely the difference of the free energy of a cloned system and the original one. I will detail the case of the mean-field p-spin spherical model, where the computation of Rényi complexities can be performed analytically via the replica trick. the Renyi complexities vanish at the Kauzmann temperature Tk, suggesting that they are a useful observable for estimating Tk in practical applications. Moreover, we show that RSB solutions are required even in the liquid phase, where interesting relationships are found between Renyi complexities and the annealed Franz-Parisi potential. (basé sur 2411.19817 )

Mercredi 5 Fevrier 2025, 14:00 à IJCLAB, 210/1-114 - Salle des Séminaires	IJCLAB-COSM (Seminar of the Gravity and cosmology group of IJCLAB)	gr-qc
Cristòbal Corral Badiola ( U. Adolfo Ibáñez )	Electric/magnetic duality of dyonic Kerr-Newman-NUT-AdS spacetimes
Abstract:	We study the (anti-)self-duality conditions under which the electric and magnetic parts of the conserved charges of the dyonic Kerr-Newman-NUT-anti-de Sitter solution become equivalent. Within a holographic framework, the stress tensor and the boundary Cotton tensor are computed from the electric/magnetic content of the Weyl tensor. The holographic stress tensor/Cotton tensor duality is recovered along the (anti-)self-dual curve in parameter space. We show that the latter not only implies a duality relation for the mass but also for the angular momentum. The partition function is computed to first order in the saddle- point approximation and a Bogomol’nyi-Prasad-Sommerfield bound is obtained. The ground state of the theory is enlarged to all the (anti-)self-dual configurations when the SO(4) and U(1) Pontryagin densities are introduced. We demonstrate this at the level of the action and variations thereof.

Mercredi 5 Fevrier 2025, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774	IPHT-HEP (Séminaire de physique des particules et de cosmologie)	hep-th
Giovanni Rizi ( IHES )	Topological constraints on defect dynamics
Abstract:	Quantum field theories (QFTs) in various dimensions can exhibit rich and complex behavior when extended objects?defects?are introduced. These defects lead to interesting dynamical phenomena that are often challenging to study directly. One of the key questions in defect quantum field theories (DQFTs) is understanding how these defects behave under renormalization group (RG) flow, as this can be complicated and difficult to analyze in many setups. In this talk, I will explore how the interplay between bulk symmetries and defects imposes non-trivial constraints on the fixed points of the RG flow. I will introduce the concept of strongly symmetric defects, which, under certain conditions, cannot decouple from the bulk theory during RG flow. Furthermore, I will define the notion of defect anomaly, akin to the ?t Hooft anomalies in conventional QFTs, which provides additional constraints on the possible IR limits of DQFTs. These ideas will be illustrated with concrete examples in 1+1 and 2+1 dimensions. Specifically I will consider the RG flow of strongly symmetric lines in 1+1 dimensional CFTs and strongly symmetric surface defects in 2+1 dimensional scalar QED. Based on 2412.18652.

Jeudi 6 Fevrier 2025, 11:00 à LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage	SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques)	hep-th
Hyeonjun Park ( KIAS )	Darboux theorem for shifted symplectic stacky fibrations
Abstract:	The Darboux theorem states that symplectic manifolds are locally cotangent bundles. An analog in derived algebraic geometry is that shifted symplectic schemes are locally twisted cotangent bundles. This can be applied to moduli spaces of sheaves on Calabi-Yau varieties, which is a crucial ingredient in Donaldson-Thomas theory. In this talk, I will present a generalization of the derived Darboux theorem to families and to stacks. As an application of the family version, I will discuss counting surfaces on CY4, which is joint work with Younghan Bae and Martijn Kool. As an application of the stacky version, I will explain the construction of cohomological Hall algebras for CY3, which is joint work with Tasuki Kinjo and Pavel Safronov. (basé sur 2406.12838 )

Jeudi 6 Fevrier 2025, 14:00 à IHES, Amphithéâtre Léon Motchane	PT-IHES (Séminaire de physique théorique de l'IHES)	hep-th
Xiangyu Cao ( LPENS )	Inflationary Inference Problem
Abstract:	In a dynamical system that incorporates an exponentially growing number of degrees of freedom, can information sent at early time be retrieved at late time? This “inflationary inference problem” arises in several contexts: statistical inference, error correction, measurement-altered quantum criticality, quantum Darwinism, and cosmology. In this talk, we will introduce the problem, and propose a general criterion for inference, extending the Kesten-Stigum threshold. Implications in some of the aforementioned contexts will be discussed. In particular, we will revisit the question of “classicalisation” during inflation.

Jeudi 6 Fevrier 2025, 14:00 à LPTMC, Jussieu, LPTMC seminar room, towers 13-12, 5th floor, room 523	SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)	cond-mat
Luca De’ Medici ( ESPCI Paris )	Insight into Hund metals and interplay with Mott physics.
Abstract:	Hund metals are paramagnetic phases in which high-spin local configurations dominate. This paradigm is now a useful guidance to interpret the physics of many transition-metal compounds, like Ruthenates and Iron-based superconductors. I will show how this physics is extremized by moving towards a half-filled Mott insulator, and that it gives rise to charge instabilities and heavy fermionic behavior along the way. A. Georges and G. Kotliar, Physics Today 77, 46 (2024) M. Chatzieleftheriou et al. Phys. Rev. Lett. 130, 066401 (2023) M. Crispino et al. ArXiv:2312.06511 (2023)

Vendredi 7 Fevrier 2025, 15:00 à LPTHE, LPTHE library	SEM-LPTHE (Séminaire du LPTHE)	hep-lat
Gabriel Lemarié ( MajuLab and CQT, CNRS-NUS, Singapore )	2D Anderson Localization belongs to KPZ Universality Class
Abstract:	In this talk, I will present our recent findings on two-dimensional Anderson localization, demonstrating its connection to the Kardar-Parisi-Zhang (KPZ) universality class. The KPZ equation describes the growth of rough interfaces. It is well-known for its universal scaling exponents and distributions, which have been found to apply to a variety of classical and quantum systems. Following early studies, our numerical analysis reveals key properties of the KPZ universality class in the fluctuations of the density logarithm of 2D Anderson localized wave packets as well as in eigenstates and the conductance logarithm. This analogy provides Anderson localization with a wealth of predictions in a regime difficult to access analytically.

Lundi 10 Fevrier 2025, 13:30 à LPENS, U209	LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)	cond-mat
Gwendal Fève ( LPENS )	TBA

Lundi 10 Fevrier 2025, 14:00 à IHES, Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )	MATH-IHES (TBA)	math
Ingrid Irmer ( SUSTech & IHES )	The Thurston Spine and Critical Points of the Systole Function on Teichmüller Space
Abstract:	Thurston defined a mapping class group-equivariant spine for Teichmüller space: the "Thurston spine". This spine is a CW complex, consisting of the points in Teichmüller space at which the set of shortest geodesics — the systoles — cut the surface into polygons. The systole function is a map from Teichmüller space to R+ whose value at any point is given by the length of the systoles. It is known that the systole function is a topological Morse function on Teichmüller space, whose critical points are contained in the Thurston spine. This talk surveys what the systole function tells us about the Thurston spine.

Lundi 10 Fevrier 2025, 16:00 à IHES, Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )	MATH-IHES (TBA)	math
Karin Melnick ( Université du Luxembourg )	Compact Lorentzian Conformally Flat Manifolds
Abstract:	Any closed, flat Riemannian manifold is finitely covered by the torus, by Bieberbach's classical theorem. Similar classifications have been pursued for closed, Riemannian conformally flat manifolds, as well as for closed, flat Lorentzian manifolds. I will present the classification of closed, Lorentzian conformally flat manifolds with unipotent holonomy. This is joint work with Rachel Lee.

Mardi 11 Fevrier 2025, 10:00 à IHES, Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz - EDP et applications )	MATH-IHES (TBA)	math
Cédric Villani ( Université Claude Bernard Lyon 1 )	Information de Fisher et régularité pour les équations de Boltzmann et Landau spatialement homogènes I

Mardi 11 Fevrier 2025, 11:30 à IHES, Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz - EDP et applications )	MATH-IHES (TBA)	math
Cyril Imbert ( CNRS & ENS )	Information de Fisher et régularité pour les équations de Boltzmann et Landau spatialement homogènes II

Mardi 11 Fevrier 2025, 14:00 à IHES, Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz - EDP et applications )	MATH-IHES (TBA)	math
Hong Wang ( New York University )	Restriction Theory and Projection Theorems

Mardi 11 Fevrier 2025, 15:30 à IHES, Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz - EDP et applications )	MATH-IHES (TBA)	math
Seung-Yeal Ha ( Seoul National University )	Recent Progress in the Mean-field Limit for the Collective Dynamics Models

Mercredi 12 Fevrier 2025, 10:30 à IHES, Amphithéâtre Léon Motchane ( Cours de l'IHES )	MATH-IHES (TBA)	math
Laure Saint-Raymond ( IHES )	Hard Sphere Dynamics in the Low Density Limit (4/4)
Abstract:	At the microscopic level, a gas is a collection of interacting neutral particles. The very large number of degrees of freedom and the sensitivity of the system to very small perturbations mean that it is essentially impossible to predict its dynamics deterministically. At the end of the 19th century, Boltzmann proposed describing the behaviour of gas in an alternative way, using a statistical approach. A natural question is whether the assumption of statistical independence that underlies this model is compatible with microscopic dynamics and in what sense the Boltzmann equation is a good approximation. This course will provide some answers to this question, within the simplified framework of contact interactions. 1. The Boltzmann equation, the chaos hypothesis and the H theorem 2. Law of large numbers for the dynamics of hard spheres 3. Correlations, dynamic clusters 4. Fluctuations and large deviations for the dynamics of hard spheres

Mercredi 12 Fevrier 2025, 13:30 à DPT-PHYS-ENS, salle ConfIV (Département de Physique de l'ENS - 24 rue Lhomond 75005 PARIS)	COLLOQUIUM-ENS (Colloquium of the Physics Department of ENS)	physics
Diamanti	TBA
Abstract:	TBA

Mercredi 12 Fevrier 2025, 13:30 à IHP, Amphi Choquet-Bruhat (batiment Perrin)	SEED (Seed Seminar of Mathematics and Physics)	math-ph
Bertrand Duplantier ( Institut de Physique Théorique, Université Paris-Saclay )	Hamiltonian Paths on Random Planar Maps
Abstract:	Hamiltonian paths are self-avoiding random walks that visit all sites of a given lattice. We consider various configuration exponents of Hamiltonian walks drawn on random planar maps. Estimates from exact enumerations are compared with predictions based on the Knizhnik-Polyakov-Zamolodchikov (KPZ) relations, as applied to exponents on the regular hexagonal lattice. Astonishingly, when the maps are bipartite, a naive use of KPZ does not reproduce all the measured exponents, but an Ansatz may possibly account for the observed discrepancies. We further study Hamiltonian cycles on various families of bipartite planar maps, which fall into two universality classes, with respective central charges c = -1 or c = -2. The first group comprises maps of fixed vertex valency p larger than 3, whereas the second group involves maps with mixed vertex valencies, as well as a so-called rigid case. For each class, a universal configuration exponent and a novel critical exponent associated with long-distance contacts along a Hamiltonian cycle are predicted from KPZ and the corresponding exponent on regular (hexagonal or square) lattices. This time, the KPZ predictions are numerically confirmed by exact enumeration results for p-regular maps, with p = 3, 4, 5, 6, 7, and for maps with mixed valencies (2,3) and (2,4). The scaling limit of fully-packed systems thus poses intriguing unresolved questions from both the Liouville Quantum Gravity and the Schramm-Loewner Evolution perspectives. Based on joint works with Ph. Di Francesco, O. Golinelli and E. Guitter.

Mercredi 12 Fevrier 2025, 14:00 à IJCLAB, 210/1-114 - Salle des Séminaires (IJCLab)	IJCLAB-COSM (Seminar of the Gravity and cosmology group of IJCLAB)	gr-qc
Aaron Held ( ENS Paris )	Numerical Relativity in effective field theories of gravity
Abstract:	The age of gravitational-wave astronomy is now in full swing: For the first time, we gain observational access to the highly dynamical strong-field regime of the gravitational interaction. Constraining potential deviations from General Relativity (GR) requires reliable waveform predictions, not just in GR, but also when higher curvature corrections contribute to the dynamics. I will present an overview of recent progress on (i) mathematical well-posedness, (ii) physical time evolution in the presence of ghosts, and (iii) numerical methods to extract nonlinear waveforms. In combination, the above constitutes a feasible pathway to use current and future gravitational-wave observations to constrain effective field theories of gravity. Items (i) to (iii) are based on three ongoing collaborations: 2407.08775, ... (with P. Figueras and A Kovacs); 2305.09631, ... (with C. Deffayet, S. Mukohyama, and A. Vikman); 2104.04010, 2306.04725, ... (with H. Lim).

Mercredi 12 Fevrier 2025, 14:45 à IHES, Amphithéâtre Léon Motchane ( Séminaire Amplitudes et Gravitation sur l’Yvette (IHES/IPhT) )	PT-IHES (Séminaire de physique théorique de l'IHES)	hep-th
Michael Saavedra ( Carnegie Mellon University )	High Energy Scattering in Classical and Quantum Gravity
Abstract:	Although the high-energy limit of gauge theory amplitudes in an old and well-studied subject, comparatively little is known about gravity. Many basic questions remain about graviton Reggeization and graviton Regge physics more broadly. More confusingly, the high-energy limit in gravity is known to coincide with the classical limit. In this talk, I will address these questions using an effective field theory for high energy scattering in gravity. In particular, I clarify the role of Regge physics in gravity and more generally address the question of resummability of large logs. Lastly, I explain the interplay between classical and Regge physics, and how one may use this to calculate large logs appearing in classical amplitudes to high loop orders.

Mercredi 12 Fevrier 2025, 15:00 à IHP, Amphi Choquet-Bruhat (batiment Perrin)	SEED (Seed Seminar of Mathematics and Physics)	math-ph
Yizheng Yuan ( Statistical Laboratory, Cambridge University, UK )	The chemical distance metric for non-simple CLE
Abstract:	We construct the continuum analogue of the chemical distance metric in lattice models such as percolation. The chemical distance metric is the graph distance induced by the percolation clusters. It is known that for critical percolation, the lengths have non-trivial scaling behaviour, however it is very difficult to find the exact scaling exponent. (This is one of the questions from Schramm's ICM 2006 article that remains unsolved.) In a joint work with Valeria Ambrosio and Jason Miller, we construct a chemical distance metric on the CLE gasket for each $\kappa\in]4,8[$. We show that it is unique metric that is geodesic, Markovian, and conformally covariant. The characterisation is reminiscent of the LQG metric, but our objects behave very differently, and hence our techniques also differ significantly from those used in LQG. For $\kappa=6$, we conjecture that our random metric space is the scaling limit of critical percolation.

Mercredi 12 Fevrier 2025, 16:15 à IHP, Amphi Choquet-Bruhat (batiment Perrin)	SEED (Seed Seminar of Mathematics and Physics)	math-ph
Léonie Papon ( Durham University, UK )	Interface scaling limit for the critical planar Ising model perturbed by a magnetic field
Abstract:	In this talk, I will consider the interface separating +1 and -1 spins in the critical planar Ising model with Dobrushin boundary conditions perturbed by an external magnetic field. I will prove that this interface has a scaling limit. This result holds when the Ising model is defined on a bounded and simply connected subgraph of $\delta\mathbb{Z}^2$, with $\delta > 0$. I will show that if the scaling of the external field is of order $\delta^{15/8}$, then, as $\delta \to 0$, the interface converges in law to a random curve whose law is conformally covariant and absolutely continuous with respect to $\text{SLE}_3$. This limiting law is a massive version of $\text{SLE}_3$ in the sense of Makarov and Smirnov and I will give an explicit expression for its Radon-Nikodym derivative with respect to $\text{SLE}_3$. I will also prove that if the scaling of the external field is of order $\delta^{15/8}g(\delta)$ with $g(\delta) \to 0$, then the interface converges in law to $\text{SLE}_3$. In contrast, I will show that if the scaling of the external field is of order $\delta^{15/8}f(\delta)$ with $f(\delta) \to \infty$, then the interface degenerates to a boundary arc.

Jeudi 13 Fevrier 2025, 10:00 à IHP, Pierre Grisvard	RENC-THEO (Rencontres Théoriciennes)	hep-th
Simone Giacomelli ( Milano-Bicocca )	4d superconformal theories from S-folds
Abstract:	In this seminar I will present a new approach to the study of 4d superconformal theories with eight supercharges. We construct a large new family of these models in string theory, study their moduli space and RG flows between them triggered by relevant deformations. Our framework provides a realization of most known theories with Coulomb branch of low dimension and suggests a new organizing principle for class S theories.

Jeudi 13 Fevrier 2025, 11:00 à IJCLAB, 210/114	IJCLAB-PTH (Particle Theory Seminar of IJCLAB Orsay)	hep-ph
Wenqi Ke ( University of Minnesota )	Recursion relations and on-shell massive amplitudes
Abstract:	As an alternative to Feynman rules, on-shell formalism offers an efficient and elegant way to compute amplitudes with arbitrary numbers of particles. This construction is based on the so-called recursion relations and relies on the choice of the momentum shift. In this talk, I present a momentum shift in the massive on- shell formalism, which allows us to construct recursively amplitudes in QED, electroweak and supergravity theories. This momentum shift is then applied to examples of $e^+e^-$, $W^+W^-$ and gravitino scatterings. One recovers the Higgs and super-Higgs mechanisms from an on-shell perspective. Finally, some future directions on higher spin Compton scatterings will be outlined.

Jeudi 13 Fevrier 2025, 11:00 à IHES, Amphithéâtre Léon Motchane ( Séminaire de Géométrie Arithmétique )	MATH-IHES (TBA)	math
Takumi Watanabe ( Université de Tokyo & IHES )	On the (phi, Gamma)-modules Corresponding to Crystalline Representations, Semi-stable Representations and de Rham Representations
Abstract:	From the 1980s to the 1990s, Jean-Marc Fontaine introduced the theory of (phi, Gamma)-modules to study p-adic Galois representations. They are simpler than p-adic Galois representations, but he showed an equivalence between them. Among p-adic Galois representations, some classes are particularly important in number theory. Main examples are crystalline representations, semi-stable representations and de Rham representations. In this talk, I will explain how we can determine the (phi, Gamma)-modules corresponding to these representations. These results can be seen, in a sense, as generalizations of Wach modules.

Jeudi 13 Fevrier 2025, 14:00 à LPTMC, campus Jussieu, couloir 12-13, 5ème étage, salle 5-23	SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)	cond-mat
Nicolas Regnault ( Flatiron institute )	Engineering quantum phases of matter through moire materials: The case of Fractional Chern insulators
Abstract:	Progress in stacking two dimensional materials, such as graphene or transition metal dichalcogenides (TMDs), has paved the way to engineer new structures relying on moire patterns. These patterns induced for example by slightly twisting one layer compared to the other, could lead to strongly correlated quantum phases such as superconductivity or the quantum anomalous Hall effects. In the realm of condensed matter physics, the fractional quantum Hall effect stands as a singular experimental manifestation of topological order, characterized by the presence of anyons—quasiparticles that bear fractional charge and exhibit exchange statistics diverging from conventional fermions and bosons. This phenomenon, observed over four decades ago, was still missing the direct observation of similar topological orders arising purely from band structure—without the application of strong magnetic fields. In 2023 within the span of a few months, several pioneering experiments have illuminated this once theoretical domain. Studies on twisted homobilayer MoTe2 and pentalayer rhombohedral graphene placed on hBN have finally unveiled the existence of fractional Chern insulators (FCIs), the zero-magnetic field analog of fractional quantum Hall states. The journey to this point, preceded by over a decade of theoretical frameworks and predictions surrounding FCIs, yet the experimental revelations have proved to be richer and more surprising than expected. In this talk, we will present how the combination of ab-initio and quantum many-body calculations can help us capture the different features observed in experiments. We will discuss the potential future for this exciting booming field, including the possible observation of fractional topological insulators, a yet-never observed topological ordered phase preserving the time reversal symmetry.

Mardi 18 Fevrier 2025, 10:30 à IHES, Amphithéâtre Léon Motchane ( Cours de l'IHES )	MATH-IHES (TBA)	math
Dustin Clausen ( IHES )	Algebraic K-theory and Chromatic Homotopy Theory (1/4)
Abstract:	The most universal kind of linear algebra is based not on abelian groups, but on homotopy-theoretic objects known as spectra. According to chromatic homotopy theory, one can systematically organize spectra into periodic families. On the other hand, a natural source of spectra is provided by algebraic K-theory, a highly refined cohomological invariant of rings (or schemes, etc). This leads to the subject of this course: the interaction of the chromatic theory with algebraic K-theory. The story begins with classical theorems of Thomason, Mitchell, and Hesselholt-Madsen. Bold generalizations of these theorems were conjectured by Rognes and Ausoni-Rognes, under the umbrella term of "redshift". Several of these conjectures are now theorems due to recent work of many people. Remarkably, this work has applications to "pure" chromatic homotopy theory: Burklund-Hahn-Levy-Schlank used it to settle (in the negative) the "telescope conjecture", the last of Ravenel's conjectures. Lecture 1: Introduction to chromatic homotopy theory. Lecture 2: Descent and "soft redshift". Lecture 3: "Hard redshift", a.k.a. the Lichtenbaum-Quillen property. Lecture 4: The telescope conjecture.

Jeudi 20 Fevrier 2025, 10:30 à IHES, Amphithéâtre Léon Motchane ( Cours de l'IHES )	MATH-IHES (TBA)	math
Dustin Clausen ( IHES )	Algebraic K-theory and Chromatic Homotopy Theory (2/4)
Abstract:	The most universal kind of linear algebra is based not on abelian groups, but on homotopy-theoretic objects known as spectra. According to chromatic homotopy theory, one can systematically organize spectra into periodic families. On the other hand, a natural source of spectra is provided by algebraic K-theory, a highly refined cohomological invariant of rings (or schemes, etc). This leads to the subject of this course: the interaction of the chromatic theory with algebraic K-theory. The story begins with classical theorems of Thomason, Mitchell, and Hesselholt-Madsen. Bold generalizations of these theorems were conjectured by Rognes and Ausoni-Rognes, under the umbrella term of "redshift". Several of these conjectures are now theorems due to recent work of many people. Remarkably, this work has applications to "pure" chromatic homotopy theory: Burklund-Hahn-Levy-Schlank used it to settle (in the negative) the "telescope conjecture", the last of Ravenel's conjectures. Lecture 1: Introduction to chromatic homotopy theory. Lecture 2: Descent and "soft redshift". Lecture 3: "Hard redshift", a.k.a. the Lichtenbaum-Quillen property. Lecture 4: The telescope conjecture.

Jeudi 20 Fevrier 2025, 11:00 à IJCLAB, 210/114	IJCLAB-PTH (Particle Theory Seminar of IJCLAB Orsay)	hep-ph
Rafael Aoude ( University of Edinburgh )	Amplitudes for Hawking Radiation
Abstract:	In this talk, I will show a new approach to compute Hawking radiation based on on-shell scattering amplitudes. The Hawking spectrum is obtained by exponentiating a series of Feynman diagrams describing a massless scalar field scattering through a collapse background. Using semiclassical methods, we obtain a generalized an in-in generalisation of an amplitude closely connected to the Bogoliubov coefficients. Finally, I will show how subdominant one-loop correction can be interpreted as finite-size corrections sensitive to the radius of the black hole.