Jeudi 21 Novembre 2024, 10:00 à IHP, Grisvard (314)	RENC-THEO (Rencontres Théoriciennes)	hep-th
Victor Godet ( LPTHE )	Quantum cosmology as automorphic dynamics
Abstract:	I will explain how some recent progress on the Wheeler-DeWitt equation makes possible the systematic development of quantum cosmology in the canonical formulation. The cosmological wavefunctions are automorphic forms, and the Wheeler-DeWitt equation reduces to a dynamical equation on moduli space, so that quantum cosmology is equivalent to "automorphic dynamics".

Jeudi 21 Novembre 2024, 11:00 à IHES, Amphithéâtre Léon Motchane ( Séminaire de Géométrie Arithmétique )	MATH-IHES (TBA)	math
Johannes Anschuetz ( Paris-Saclay et IHES )	Pro-étale Cohomology in p-adic Geometry
Abstract:	Pro-étale cohomology of rigid-analytic varieties over the p-adic complex numbers has surprising features, which can be explained by calculating the pro-étale cohomology via quasi-coherent sheaves on the Fargues-Fontaine curve. In this talk I want to explain the recent construction of a 6-functor formalism with values in quasi-coherent sheaves on the Fargues-Fontaine curve, and to discuss some of its properties. This is joint work with Arthur-César Le Bras and Lucas Mann.

Jeudi 21 Novembre 2024, 11:45 à IHP, Grisvard (314)	RENC-THEO (Rencontres Théoriciennes)	hep-th
Ian Moult ( Yale )	Energy Correlators at the Collider Frontier
Abstract:	Correlation functions of the average null energy (ANE) operator provide a direct link between quantum field theory and collider physics observables. We will discuss recent advances in our understanding of these correlation functions, and show that they can be directly measured in real collider data. We then discuss several applications of recent measurements, ranging from precision extractions of the strong coupling constant from the scaling properties of light-ray operators, to characterizing the quark gluon plasma with higher twist light-ray operators.

Jeudi 21 Novembre 2024, 14:00 à LPTMC, campus Jussieu, couloir 12-13, 5ème étage, salle 5-23	SEM-EXCEP (Seminaire exceptionnel)	cond-mat
Francesco Mori ( Oxford )	Optimal strategies in navigation and learning: statistical physics meets control theory
Abstract:	To survive, animals must acquire a diverse set of skills and integrate them to respond effectively to complex environments. For instance, to move in a straight line in rough terrains, dung beetles alternate between egocentric strategies, maintaining an internal estimate of position, and geocentric strategies, using landmarks for trajectory correction. In the first part of this talk, I will consider this behaviour within a minimal model of navigation and derive the switching strategy that maximises speed, accounting for environmental, execution, and sensory noise. In the second part of the talk, I will consider the complementary problem of learning multiple skills/tasks, a.k.a., continual learning. While animals typically excel at continual learning, artificial neural networks often forget older tasks when new ones are introduced. By combining exact training dynamics from statistical physics with optimal control methods, I will derive strategies that optimise performance while avoiding forgetting. This flexible framework reveals interpretable strategies in multi-task learning and can be adapted to optimise high-dimensional learning processes. References: arXiv:2311.18813 and arXiv:2409.18061

Jeudi 21 Novembre 2024, 14:00 à LPTM, 4.13b	SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise)	math-ph
Mathieu Lewin ( CEREMADE Université Paris Dauphine-PSL )	Mathematical Challenges in Density Functional Theory
Abstract:	Schrödinger's equation fits on just one line and it is supposed to accurately describe the behavior of most atoms and molecules of our world. But it is essentially impossible to simulate to a high precision, due to its very high dimensionality. In this talk I will give a general overview of Density Functional Theory (DFT), which is the main technique used nowadays to approximate Schrödinger's equation for electrons. I will then discuss the mathematical structure of DFT and mention a few results obtained in collaboration with Elliott Lieb and Robert Seiringer.

Vendredi 22 Novembre 2024, 11:00 à IJCLAB, 100/2-A201 - Salle A201 (IJCLab) ( https://indico.ijclab.in2p3.fr/event/11180/ )	IJCLAB-HEP (Particle Physics Seminars at IJCLab)	hep-ph
Hagop Sazdjian ( IJCLab )	Scattering of mesons and emergence of tetraquarks in two-dimensional QCD
Abstract:	Scattering of two mesons is considered in the framework of two-dimensional QCD in the large-$N_c$ limit with four different quark flavors. The scattering takes place through two coupled channels, corresponding to direct and quark-exchange processes. Infrared finiteness of the scattering amplitudes to order $1/{N_c}^2$ is shown. The theory reduces, at low energies, to an effective theory of mesons, interacting by a quark-exchange process, by means of a contact term. The unitarization of the scattering amplitudes leads to the emergence of a tetraquark bound state.

Lundi 25 Novembre 2024, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774	IPHT-PHM (Séminaire de physique mathématique)	math-ph
Frédéric Van Wijland ( MSC, Univ. Paris Cité )	Sampling the Boltzmann distribution, ever faster
Abstract:	Sampling a given target distribution is a ubiquitous problem in physics, which can prove very hard (hard means slow) in some well documented systems where the energy landscape features a host of local minima, at least at low temperatures. Hence the necessity to find ways and means to speed the sampling up to bypass the natural sluggishness of the physical dynamics in these systems. We will consider the worst possible physical system --a glass forming liquid-- and subject it to various acceleration techniques corresponding to distinct time evolutions, the efficiency of which will be critically discussed. We will then use this variety of time evolutions to take a step back and reflect on the nature of the glass transition. We shall conclude by proposing a picture in which seemingly contradicting theories of glasses can be reconciled. In collaboration with F. Ghimenti, L. Berthier, J. Kurchan and G. Szamel.

Lundi 25 Novembre 2024, 11:00 à IHES, Amphithéâtre Léon Motchane	MATH-IHES (TBA)	math
Sean Howe ( University of Utah )	Inscription and p-adic Periods
Abstract:	We introduce a category of inscribed v-sheaves as a minimal differential extension of the theory of diamonds in p-adic geometry, then explain how to apply this theory to differentiate natural period maps in p-adic Hodge theory.

Lundi 25 Novembre 2024, 14:00 à LPNHE, Amphi Charpak	LPNHE (Séminaires du LPNHE)	physics
Takis Kontos ( LPENS )	Quantum sensing of axion dark matter with a phase resolved haloscope
Abstract:	Axions are hypothetical particles which do not belong to the standard model and are considered as good candidates to explain the dark matter in the Universe. As first proposed by P. Sikivie in 1983, it may be possible to detect them using a microwave cavity under a large magnetic field. Such a device is called a haloscope. We have developed a new type of haloscope. It combines a superconducting quantum circuit, an antiferromagnetic crystal in addition to the microwave cavity. It aims to detect the axion signal by measuring a phase shift of the microwave signal. Furthermore, the antiferromagnetic crystal provides a tunability, enabling in principle a large mass scanning range. It is expected to have an unprecedented figure of merit and mass scanning range. In my talk, I will present both the concept and the first experimental results of our haloscope.

Mardi 26 Novembre 2024, 10:45 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
Marcelo Guzmán ( Université de Pennsylvanie )	Learning functionality under physical constraints: how physics shapes the way machines learn
Abstract:	From biological systems to neuromorphic computing, learning is fundamentally constrained by physics. These constraints, ranging from optimization principles (e.g., energy minimization) to conservation laws and stochastic dynamics in the presence of noise, shape learning dynamics and learned functions in ways absent in artificial neural networks (ANNs). In this two-part talk, I explore how physical constraints influence learning by examining two paradigmatic physical learning models: tunable mechanical networks and self-learning resistor networks. First, I will show that learning in these physical networks is a dual optimization problem. In the case of resistor networks, for example, it is the minimization of a cost with respect to conductances and the minimization of the power dissipated with respect to voltages—the physical constraint. This additional minimization couples cost and power, enabling inference of key network components through simple physical measurements. I will demonstrate that the high-curvature directions around the cost minima —highlighting the key functional components— are captured by the network’s physical susceptibilities. These susceptibilities, encoded in the softest modes of the power, are measurable and provide clear insights into the network’s functionality, suggesting an interpretability advantage over ANNs and a new framework for studying biological systems for which the cost is unknown. Next, I will focus on the local dynamics of self-learning resistor networks in laboratory settings. Learning in these systems is the outcome of the collective behavior of individual components. While these networks are energy-efficient, they are sensitive to the presence of external noise and internal biases, two physical constraints. I will show how noise and bias affect the learning dynamics when training for two periodically alternating tasks. In ideal conditions, periodic training converges to an optimal solution for both tasks. However, in the presence of noise and bias, learning leads to limit cycles in the space of conductances. Based on theory and experiments, I uncover a complex interplay between the geometry of the solution space (linked to task complexity), bias, and noise, revealing distinct learning phases in terms of the training period. Finally, I will show that under certain conditions, bias can improve the networks’ learning capabilities.

Mardi 26 Novembre 2024, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774	IPHT-HEP (Séminaire de physique des particules et de cosmologie)	hep-ph
Gabriele Franciolini ( CERN )	Searching for Subsolar Mass Primordial Black Holes with Gravitational Waves
Abstract:	Primordial black holes (PBHs) can form in the early universe and represent an intriguing dark matter candidate as well as a unique probe of the physics governing the early universe. Focusing on subsolar mass PBHs, we will discuss avenues to constrain their abundance with gravitational waves (GWs). These include i) direct searches for mergers using LIGO/Virgo/Kagra detectors

Mardi 26 Novembre 2024, 14:00 à LPENS, L378, 24 Rue Lhomond	LPTENS-HE (Séminaire commun LPTENS-LPTHE)	hep-th
Nika Sokolova ( King's College London )	Probing Excited Strings on AdS5 × S5 via Integrability and Conformal Bootstrap.
Abstract:	We study the CFT data of planar 4D N=4 Super-Yang-Mills in the strong 't Hooft coupling limit, focusing on massive short strings in the flat-space limit of AdS5 ×S5. Specifically, we analyse the string states exchanged in the OPE of a four-point function dual to the AdS Virasoro-Shapiro amplitude. By organising this data into Regge trajectories, we predict the leading-order behaviour of four subleading trajectories using integrability, analyticity, and recent advances on the Virasoro-Shapiro amplitude. Notably, one trajectory and entire Kaluza-Klein towers decouple in the flat-space limit, hinting at an emergent selection rule for short-string scattering. Based on arXiv:2409.07529, arXiv:2310.06041, and arXiv:2306.12379.

Mardi 26 Novembre 2024, 14:00 à LPTHE, Library	LPTHE-PPH (Particle Physics at LPTHE)	hep-ph
Ben Allanach ( DAMTP Cambridge )	TBA
Abstract:	TBA

Mercredi 27 Novembre 2024, 11:00 à LKB, Sorbonne Université - 4 places Jussieu 75005 - Amphi Charpak	SEM-LKB (Séminaire du Laboratoire Kastler Brossel)	quant-ph
Jean-Philippe Brantut ( EPFL )	Quantum simulations with atoms and photons
Abstract:	Cavity quantum electrodynamics (QED) is one of the most powerful frameworks to observe and leverage quantum phenomena. While it has been thoroughly studied for simple quantum systems such as two-level systems or harmonic oscillators, it has only recently become available for complex, correlated quantum many-body systems. In the last years, we have developed systems combining cavity QED with cold Fermi gases. In this talk, I will describe these setups, and some of the intriguing consequences of the interplay of strong atom-atom and strong light-matter coupling. I will then present the use of the cavity to induce long-range interactions between, and review some of the spectacular consequences on the state of the gas. Last, I will outline the perspectives open by the convergence of cavity QED with complex quantum matter, in particular the possibility of programming cavity-mediated interactions, and the application of these ideas for condensed matter and high-energy physics.

Mercredi 27 Novembre 2024, 12:45 à LPENS, 3 rue dUlm College de France	FORUM-ENS (Forum de Physique Statistique @ ENS)	cond-mat.stat-mech
Giulio Biroli ( ENS )	TBA

Jeudi 28 Novembre 2024, 11:00 à LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage	SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques)	hep-th
David Hernandez ( IMJ-PRG )	Folded quantum integrable models, deformed W-algebras and representations of quantized Coulomb branches
Abstract:	Deformed W-algebras are two parameter algebras associated to a simple Lie algebra g, obtained from fields commuting with screening operators. We discuss some remarkable specializations of deformed W-algebras. (1) Classical limit : We propose a novel quantum integrable model for every non- simply laced simple Lie algebra g (joint work with Frenkel and Reshetikhin). Its spectra correspond to solutions of the Bethe Ansatz equations obtained by folding the Bethe Ansatz equations associated to the simply-laced Lie algebra g′ (corresponding to g). Our construction is motivated by the analysis of the second classical limit of the deformed W-algebra of g. We conjecture, and verify in a number of cases, that the spaces of states of the folded integrable model can be identified with finite-dimensional representations of the Langlands dual (twisted) quantum affine algebra. (2) Mixed limit : we use this limit to state a general conjecture on the parametrization of simple modules of non simply-laced shifted quantum affine algebras (closely related to quantized Coulomb branches). We have several evidences, including a general result for simple finite-dimensional representations.

Jeudi 28 Novembre 2024, 14:00 à LPENS, E378	SEM-EXCEP (Seminaire exceptionnel)	cond-mat.stat-mech
Chunxiao Liu ( UC Berkeley )	Crystallography, Group Cohomology, and Lieb-Schultz-Mattis Constraints
Abstract:	We compute the mod-2 cohomology rings for three-dimensional (3D) space groups and establish a connection between them and the lattice structure of crystals with space group symmetry. This connection allows us to obtain a complete set of Lieb-Schultz-Mattis constraints, specifying the conditions under which a unique, symmetric, gapped ground state cannot exist in 3D lattice magnets. We associate each of these constraints with an element in the third mod-2 cohomology of the space group, when the internal symmetry acts on-site and its projective representations are classified by powers of Z2. We demonstrate the relevance of our results to the study of U(1) quantum spin liquids on the 3D pyrochlore lattice. We determine, through anomaly matching, the symmetry fractionalization patterns of both electric and magnetic charges, extending previous results from projective symmetry group classifications. (basé sur 2410.03607 )

Jeudi 28 Novembre 2024, 17:00 à UFR-PHYS-SU, Amphi 25 Campus Pierre-et-Marie-Curie, Jussieu	CPMC (Colloquium Pierre et Marie Curie)	astro-ph|cond-mat|gr-qc|hep-ex|hep-lat|hep-ph|hep-th|physics|quant-ph
Alberto Loarte ( Head of ITER Science Division )	ITER: objectives, status and physics of nuclear fusion plasmas
Abstract:	TBA

Lundi 2 Décembre 2024, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774	IPHT-STA (Séminaire de Physique Statistique, CEA/Saclay)	cond-mat
Amit Goshal ( Indian Institute of Science Education and Research Kolkata )	TBA

Lundi 2 Décembre 2024, 14:00 à LPNHE, Amphi Charpak	LPNHE (Séminaires du LPNHE)	physics
Zaki Leghtas ( LPENS )	Vers l'ordinateur quantique : un qubit de chat de Schrödinger à long temps de vie
Abstract:	Quantum computers might be capable of solving computational problems that are intractable to classical computers. Common examples are the simulation of chemical reactions or exotic materials. In the last two decades, the progress towards building a quantum computer has been outstanding. In the early 2000s, physicists were learning how to build and control single quantum bits : the elementary system that encodes a single bit of quantum information, also known as "qubit". In 2024, chips of hundreds of qubits are now available, that even outperform classical computers on very specific tasks. In this seminar, I will describe the hopes and challenges in building a quantum computer. I will delve into a particularly successful platform for quantum computing, known as superconducting circuits. Finally, I will describe some of my own research on constructing a "Schrödinger cat-qubit", a promising candidate for universal quantum computing [Nature 629 778-783 (2024)].

Mardi 3 Décembre 2024, 10:45 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
Marc Hütt ( Bremen, Germany )	TBA

Mercredi 4 Décembre 2024, 10:30 à IHES, Amphithéâtre Léon Motchane	SEED (Seed Seminar of Mathematics and Physics)	math-ph
Francesco Russo ( University of Pisa & INFN )	Partial Wave Decomposition in Thermal Conformal Field Theories
Abstract:	The conformal block expansion of correlation functions is a fundamental tool in the bootstrap program. Block computation can be related to a specific class of harmonic functions on the conformal group. We generalise this concept to the case of thermal conformal field theories and compute one-point blocks for spinning representations in three dimensions. Specifically, we derive a universal Casimir equation and solve it using recursion relations. Finally, we use the blocks in several examples to explore some features of OPE coefficients.

Mercredi 4 Décembre 2024, 11:00 à LKB, Sorbonne Université - 4 places Jussieu 75005 - Amphi Charpak	SEM-LKB (Séminaire du Laboratoire Kastler Brossel)	quant-ph
Sebastian Hofferberth ( University of Bonn )	Rydberg Quantum Optics with Ultracold Ytterbium
Abstract:	Rydberg quantum optics exploits the Rydberg blockade effect in atomic ensembles to create an effective interaction between individual optical photons. Coherent mapping of the Rydberg interaction between atoms onto photons propagating through the medium has enabled the realization of photon-photon gates, single-photon level circuit components such as optical transistors and switches and the study of strongly correlated few-body systems of photons. To date experiments have used alkali atomic species such as Rb or Cs, because of well-established laser cooling and manipulation techniques. Earth-alkaline-(like) atoms such as Sr or Yb offer unique new properties both for initial cooling and trapping as well as novel Rydberg physics. In particular, bosonic Yb offers an ideal level scheme for Rydberg quantum optics, with well-matched excitation wavelengths and the complete absence of fine- and hyper-fine structure in Rydberg S-states. In this talk I will give an overview on Rydberg quantum optics and present some results from our group, such as the observation of three-photon collisions and deterministic photon-subtraction. I will then present our new effort employing ultracold Yb for Rydberg physics. I will present our experiment apparatus combining fast production of laser-cooled Yb with Rydberg excitation and single-photon & -ion detection, as well as our first observations of Rydberg-physics in Yb.

Mercredi 4 Décembre 2024, 12:00 à IHES, Amphithéâtre Léon Motchane	SEED (Seed Seminar of Mathematics and Physics)	math-ph
Nafiz Ishtiaque ( IHES )	Kramers-Wannier Duality in Non-abelian Ising Models from SymTFT
Abstract:	I will present a concrete construction of 2d Ising partition functions on lattice, with non-abelian (more generally non-invertible) global symmetry. The construction realizes the Ising model as the boundary theory of a 3d symmetry topological field theory (SymTFT) with specific boundary conditions. Suitable choices of boundary conditions correspond to going to different topological sectors of the global symmetry or gauging arbitrary non-anomalous subsymmetry. Electric-magnetic type duality of the SymTFT results in dual descriptions of the Ising model that generalizes the Kramers-Wannier duality of Z/2Z symmetric Ising models.

Mercredi 4 Décembre 2024, 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
Christos Panagopoulos ( Nanyang Technological University, Singapore )	An Elegant Twist on Condensed Matter
Abstract:	We are generally more familiar with the beauty of images that showcase the natural world than with the beauty inside materials. Advances in theoretical insights, experimental techniques, and reconstruction algorithms, however, now allow us to explore this elegance in fine detail. For example, polymers and ferroelectric ceramics host twist patterns; chiral liquid crystals display patterns of molecular orientation; and magnetic materials exhibit axisymmetric whirls of spin. The talk will gradually focus on helical magnetic textures and their viability to influence a superconductor for adaptable recipes for quantum operations. But also, our efforts to quantize helicity, joining the likes of electrical charge and light.

Jeudi 5 Décembre 2024, 11:00 à IHES, Amphithéâtre Léon Motchane ( Séminaire de géométrie arithmétique )	MATH-IHES (TBA)	math
Luca Barbieri Viale ( Université de Milan et IHES )	Universal Weil Cohomology versus Grothendieck’s Standard Conjectures
Abstract:	The universal Weil cohomology (obtained in a recent work jointly with B. Kahn) is taking values in an abelian Q-linear (Q is the field of rational numbers) tensor category M which is rigid but its Q-algebra E = End (1) of endomorphisms of the unit is not a field, a priori. André’s theory of motivated cycles MA, in characteristic zero, can be recovered via the universal Weil cohomology as a localisation of M; thus E = Q if and only if M = MA is André’s category which is then universal for all Weil cohomologies taking values in abelian Q-linear rigid tensor categories. A similar picture holds true for the universal mixed Weil cohomology with values in MM with respect to Nori motives NM. However, in any characteristic, this new Weil cohomology yields a universal homological equivalence hum and a canonical comparison faithful tensor functor F from Grothendieck motives (modulo hum) MG to M. This F is an equivalence if and only if MG is abelian, F is exact and the Grothendieck Lefschetz standard conjecture holds true. Moreover, F is an equivalence with M semi-simple if and only if hum is numerical equivalence. Therefore Grothendieck’s standard conjectures for the universal Weil cohomology or the stronger Voevodsky’s nilpotence conjecture (independently of any Weil cohomology) imply that E = Q. A standard hypothesis is then that this absolutely flat Q-algebra E is a domain hence a field. This hypothesis is equivalent to the property that M is Tannakian. Similarly, for MM. Note that, for every self correspondence, the trace and the Lefschetz number (as well as the coefficients of the characteristic polynomials) are defined over E. As a consequence, if E is a field all these are the same independently of the Weil cohomology.

Vendredi 6 Décembre 2024, 14:00 à LPTHE, Library and Zoom (link in the comments)	LPTHE-PPH (Particle Physics at LPTHE)	hep-ph
Pearl Sandick ( University of Utah )	TBA
Abstract:	TBA

Lundi 9 Décembre 2024, 13:30 à LPENS, L378	LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)	cond-mat
Vyacheslavs Kashcheyevs ( LU )	Strong non-linearity regime of electron quantum optics

Lundi 9 Décembre 2024, 14:00 à LPNHE, Amphi Charpak	LPNHE (Séminaires du LPNHE)	physics
Axel Arbet-Engels ( Max Planck Institute for Physics )	Unraveling the particle dynamics in Active Galactic Nuclei via multi wavelength photometry and polarimetry of bright blazars
Abstract:	Active Galactic Nuclei (AGNs) are among the most powerful persistent particle accelerators in our universe. Despite decades of investigations, AGNs are still far from being understood. Because they are prime candidate sources of ultra- high-energy cosmic rays and high-energy neutrinos, their understanding is key in the current era of multi-messenger astronomy. The advent of new instrumentation for photon and neutrino astronomy brings new scientific capabilities to probe the underlying physics of these cosmic accelerators. Among all AGNs, the best candidates to probe the evolution of the particle distribution are blazars that are nearby and bright throughout the electromagnetic spectrum. I will summarize the current knowledge of AGN physics and present recent results from our multiwavelength programs of nearby AGNs making use, for the first time, of X-ray polarisation thanks to the IXPE satellite. I will discuss how such results provide powerful insights on the acceleration process, even if a high degree of complexity is revealed. The next step is to validate theoretical models (and the related dynamics) with dedicated simulations for particle acceleration and temporal evolution.

Mardi 10 Décembre 2024, 10:45 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
Thibault Congy ( Northumbria University, UK )	TBA