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X-WR-CALNAME:Département de mathématiques et applications
X-ORIGINAL-URL:https://www.math.ens.psl.eu
X-WR-CALDESC:évènements pour Département de mathématiques et applications
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TZID:Europe/Paris
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20260329T010000
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TZOFFSETFROM:+0200
TZOFFSETTO:+0100
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DTSTART:20261025T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260504T160000
DTEND;TZID=Europe/Paris:20260504T170000
DTSTAMP:20260608T155700
CREATED:20260504T074450Z
LAST-MODIFIED:20260504T074451Z
UID:21610-1777910400-1777914000@www.math.ens.psl.eu
SUMMARY:Thomas Serafini
DESCRIPTION:.
URL:https://www.math.ens.psl.eu/evenement/thomas-serafini/
LOCATION:Salle W
CATEGORIES:Colloquium doctorant
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260506T110000
DTEND;TZID=Europe/Paris:20260506T120000
DTSTAMP:20260608T155700
CREATED:20260430T081744Z
LAST-MODIFIED:20260430T081744Z
UID:21515-1778065200-1778068800@www.math.ens.psl.eu
SUMMARY:Matteo Tamiozzo\, raconte-moi les groupes de Golod-Shafarevich !
DESCRIPTION:Les groupes de Golod-Shafarevich\, découverts dans les années 60\, ont trouvé des applications en théorie des nombres\, théorie des groupes et topologie. Dans cet exposé j’introduirai ces groupes\, et j’expliquerai le rôle qu’ils jouent dans l’étude des groupes fondamentaux des anneaux des entiers des corps de nombres et des variétés de dimension 3.
URL:https://www.math.ens.psl.eu/evenement/matteo-tamiozzo-raconte-moi-les-groupes-de-golod-shafarevich/
LOCATION:Salle W toits du DMA
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260506T131500
DTEND;TZID=Europe/Paris:20260506T141500
DTSTAMP:20260608T155700
CREATED:20260401T122545Z
LAST-MODIFIED:20260507T091846Z
UID:21204-1778073300-1778076900@www.math.ens.psl.eu
SUMMARY:Exemples d'approches de statistique pour le traitement de signal et les sciences du vivant
DESCRIPTION:Je présenterai dans cet exposé deux approches statistiques pour résoudre deux problèmes très différents : l’un en traitement du signal et l’autre en sciences du vivant. Plus précisément\, dans la première partie de cet exposé\, je présenterai un test de détection de rupture pour faire de la détection d’anomalies dans le trafic internet et dans la deuxième partie\, je présenterai une approche régularisée pour analyser des données de biologie moléculaire. \n\n\n\n\n\n\n\nSéminaires des Mathématiques
URL:https://www.math.ens.psl.eu/evenement/celine-levy-leduc/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:ANNÉE 2025-2026,Séminaire Des mathématiques
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260506T140000
DTEND;TZID=Europe/Paris:20260506T170000
DTSTAMP:20260608T155700
CREATED:20260430T080415Z
LAST-MODIFIED:20260430T081156Z
UID:21503-1778076000-1778086800@www.math.ens.psl.eu
SUMMARY:Un après-midi de théorie des groupes - Elia Fioravanti\, Enrico Le Donne\, Catherine Pfaff
DESCRIPTION:14.00 – 14.45   Elia Fioravanti (KIT – Karlsruhe) « Generators for automorphisms of special groups »15.00 – 15.45   Enrico Le Donne (University of Fribourg) « Asymptotic geometry of Riemannian nilpotent groups »16.15 – 17.00   Catherine Pfaff (Queen’s University) « A « cubist » decomposition of the Handel-Mosher axis bundle » \n\n\n\n \n\n\n\nAbstracts: \n\n\n\nElia Fioravanti: Generators for automorphisms of special groups  \n\n\n\nGiven a family F of finitely generated groups\, do all groups in F have “tame” automorphisms\, or can there be “wild” examples? More concretely\, is Out(G) finitely generated for all groups G in the family F? Rips and Sela showed in the 90s that Out(G) is finitely generated for all Gromov-hyperbolic groups G\, while Baues and Grunewald showed in the 00s that Out(G) is arithmetic over Q (and hence finitely generated) for all virtually polycyclic groups G. This essentially exhausts our limited understanding of general phenomena of this kind\, with the structure of automorphisms of non-positively curved groups remaining a fundamental open problem. I will discuss the recent result that Out(G) is finitely generated for all (cocompact) special groups of Haglund and Wise. This is already new for most finite-index subgroups of right-angled Artin and Coxeter groups. \n\n\n\nEnrico Le Donne: Asymptotic geometry of Riemannian nilpotent groups. \n\n\n\nAsymptotic cones of Riemannian nilpotent Lie groups are Carnot groups. The volume of balls in Carnot groups grows exactly as a power of the radius. Heuristically\, the better the asymptotic cone approximates a Riemannian group\, the closer the volume growth approaches a polynomial growth. I will discuss several results obtained over the last few years in collaboration with Breuillard\, Nalon\, Nicolussi Golo\, and Ryoo. \n\n\n\nCatherine Pfaff: A “cubist” decomposition of the Handel-Mosher axis bundle \n\n\n\nA hyperbolic isometry acts on the compactified hyperbolic plane with North-South dynamics and a single invariant axis. The same is true for a pseudo-Anosov mapping class acting on a Teichmuller space and other hyperbolic-like settings. However\, while a fully irreducible free group outer automorphism acts on compactified Outer space with North-South dynamics\, there can be many axes for a single fully irreducible φ ∈ Out(F_r). With this in mind\, Handel and Mosher define the axis bundle for a fully irreducible φ ∈ Out(F_r). And then Handel-Mosher and Bridson-Vogtmann ask about the geometry of the axis bundle. In joint work with Chi Cheuk Tsang\, we show that the axis bundle of a nongeometric fully irreducible outer automorphism admits a canonical “cubist” decomposition into branched cubes that fit together with special combinatorics. From this structure\, we locate a canonical finite collection of periodic fold lines in each axis bundle. This can be considered as an analogue of results of Hamenstadt and Agol from the surface setting\, which state that the set of trivalent train tracks carrying the unstable lamination of a pseudo-Anosov map can be given the structure of a CAT(0) cube complex\, and that there is a canonical periodic fold line in this cube complex. Our “cubist” decomposition also gives a “hands on” solution to the fully irreducible
URL:https://www.math.ens.psl.eu/evenement/un-apres-midi-de-theorie-des-groupes-elia-fioravanti-enrico-le-donne-catherine-pfaff/
LOCATION:Salle W
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260507T110000
DTEND;TZID=Europe/Paris:20260507T120000
DTSTAMP:20260608T155700
CREATED:20260430T081020Z
LAST-MODIFIED:20260430T081021Z
UID:21505-1778151600-1778155200@www.math.ens.psl.eu
SUMMARY:Gauthier Thurin\, Valérie Castin
DESCRIPTION:Gauthier Thurin – « Convergence Rates for Distribution Matching with Sliced Optimal Transport »Valérie Castin – « Balanced Low-Rank Adaptation: Removing Parameter Invariance to Accelerate Convergence »
URL:https://www.math.ens.psl.eu/evenement/gauthier-thurin-valerie-castin/
LOCATION:Salle W
CATEGORIES:CSD seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260511T110000
DTEND;TZID=Europe/Paris:20260511T120000
DTSTAMP:20260608T155700
CREATED:20260507T082804Z
LAST-MODIFIED:20260507T082805Z
UID:21697-1778497200-1778500800@www.math.ens.psl.eu
SUMMARY:Brune Massoulié - An introduction to some self-repelling processes.
DESCRIPTION:Self-repelling walks and processes are stochastic processes that are influenced by their past behaviour\, in a way that makes them try to avoid their past trajectory. In this talk\, I will first present a toy model for self-repelling random walks introduced by Toth and Werner\, which allows to present results and methods that generalise to more complex models. I will then present the « true » self-avoiding walk (TSAW) and state the results from an article by Toth in 1995. Last\, I will informally present the « true » self-repelling motion\, which was constructed by Toth and Werner in 1998\, and was proved to be the limit of the TSAW very recently by Kosygina and Peterson.
URL:https://www.math.ens.psl.eu/evenement/brune-massoulie-an-introduction-to-some-self-repelling-processes/
LOCATION:Salle W (ENS)
CATEGORIES:Séminaire informel de probabilités
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260513T110000
DTEND;TZID=Europe/Paris:20260513T120000
DTSTAMP:20260608T155700
CREATED:20260511T082240Z
LAST-MODIFIED:20260511T082240Z
UID:21721-1778670000-1778673600@www.math.ens.psl.eu
SUMMARY:Amina Abdurrahman\, raconte-moi la topologie arithmétique !
DESCRIPTION:J’esquisserai comment des outils topologiques peuvent être utilisés dans la preuve de résultats arithmétiques en me concentrant sur les fonctions zêta en arithmétique et en topologie.En particulier\, je donnerai une formule cohomologique pour les fonctions L symplectiques du côté arithmétique\, dont la preuve repose de manière cruciale sur une formule similaire pour la torsion de Reidemeister des variétés de dimension 3 du côté topologique. Je donnerai également une perspective topologique sur l’ordre du groupe de Tate-Shafarevich.
URL:https://www.math.ens.psl.eu/evenement/amina-abdurrahman-raconte-moi-la-topologie-arithmetique/
LOCATION:Salle W toits du DMA
CATEGORIES:Algèbre et géométrie,Séminaire Raconte-moi
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260518T000000
DTEND;TZID=Europe/Paris:20260520T235959
DTSTAMP:20260608T155700
CREATED:20260507T090720Z
LAST-MODIFIED:20260507T090939Z
UID:21709-1779062400-1779321599@www.math.ens.psl.eu
SUMMARY:Recent Progress on Self-Interacting Processes and Non-Reversible Monte Carlo
DESCRIPTION:Toutes les informations de la conférence sur la page de l’évènement \nAnthony Maggs: Large scale dynamics of non-reversible Monte Carlo algorithmsMonte Carlo simulation is a workhorse of the numerical study of physical systems at thermodynamic equilibrium. Non-reversible Monte Carlo algorithms replace the commonly used constraint of detailed balance with global balance. We give examples of situations where this leads to accelerated sampling of physical systems. We argue that the large-scale relaxation of such Event-Chain Monte Carlo methods is linked to the dynamics of the true self-avoiding walk. \nFrancis Lörler: Event Chain Monte Carlo\, self-repellent random walks\, and the stochastic heat equationThe Event Chain Monte Carlo algorithm is an MCMC method for sampling equilibrium configurations of interacting particles. When applied to a harmonic chain of oscillators\, it is closely related to the self-repellent random walk on a discrete circle. We show that these processes are second-order lifts of a discrete stochastic heat equation with additive noise. As a consequence\, we obtain a lower bound on the relaxation times of order n^{3/2}. Moreover\, we show that when the active particle is resampled with an appropriate rate\, then the relaxation time has an upper bound of order n^2. On the same model\, optimally tuned Hamiltonian Monte Carlo achieves a relaxation time of order n^{5/4}\, but due to the gradient evaluations\, its complexity is of order n^{9/4}. This confirms a conjecture of Werner Krauth that on this specific model\, ECMC can outperform HMC. Joint work with Andreas Eberle. \nBrune Massoulié: From the lifted TASEP to true self-avoiding walksThe lifted TASEP is a variant of the totally asymmetric exclusion process where at each time-step\, instead of trying to move forward a uniformly chosen particle\, a marked particle tries to move forward then may pass the marker to another particle. It was introduced by physicists as a toy model for non-reversible event-chain Monte-Carlo algorithms\, which are expected to reach equilibrium faster than reversible dynamics. We will study the behaviour of this system on the integer line by evidencing a connection with true self-avoiding walks\, yielding timescales of the dynamics. This is based on joint work with Clément Erignoux\, Werner Krauth\, François Simenhaus and Cristina Toninelli. \nFrancesco Coghi and Juan Garrahan: Self-interacting processes: from tensor networks to level 2.5 large deviationsIn this combined presentation\, we discuss two aspects of self-interacting processes (stochastic processes whose transition rates depend on empirical observables). First we show\, using a tensor network approach\, a connection to Doob conditioning\, such that Markov processes with constrained occupation measures are optimally realised by self-interacting dynamics. Second\, exploiting a natural separation of timescales\, we formulate the exact large deviation statistics for the joint empirical measure and flux\, thus extending the classical Markov theory to this non-Markovian setting. \nJonathon Peterson: Limit Theorems for self-interacting random walks: a Ray-Knight approachIn this talk I will discuss recent results\, joint with Kosygina\, Mareche\, and Mountford\, which show how one can use “joint Ray-Knight theorems” to prove functional limit laws for certain self-interacting random walks. Recent results of myself and co-authors have used these techniques to prove scaling limits for the “true” self-avoiding random walk and also for polynomially self-repelling random walks. For “true” self-avoiding walks we confirm a conjecture of Toth and Werner that the scaling limit is the “true” self-repelling motion. For polynomially self-repelling walks the scaling limit is a new process (the polynomially self-repelling motion) which has the same marginal distributions as a (1/2\, 1/2)-Brownian motion perturbed at its extrema\, but which has different joint distributions. \nLaure Marêché: Limit behavior for the self-repelling random walk with directed edgesThe self-repelling random walk with directed edges on Z was introduced by Tóth and Vető in 2008. It is a random walk with a memory\, such that the probability to cross a directed edge of Z is smaller if this edge was already crossed a lot in the past. Its definition resembles that of the more studied self-interacting random walks introduced by Tóth in 1994\,1995\,1996\, with directed edges instead of undirected edges. However\, this seemingly minor change yields a sharp difference in the behavior of the walk\, and the self-repelling random walk with directed edges on Z turns out to have very unusual properties\, which we will present in this talk. \nJulien Brémont: The memory of geometry in self-interacting random walks : eccentricity and flip statisticsObserving a particular set of visited sites strongly impacts the future for a self-interacting random walk\, as it conditions the past trajectory in a certain way. In one dimension\, the geometry of the past visited territory is described by the number of visited sites n\, and the eccentricity z\, that is the fraction of positive visited sites. How a certain geometry (n\,z) condition the future set of visited sites is a key question in understanding the impact of the past on future exploration. In this talk\, I will show how to answer this question for one-dimensional self-interacting random walks ; in particular\, I will use the Brownian web to compute the distribution of future geometry (n’\, z’) given (n\, z). \nPaul Pineau: Collective Behavior of Self-Interacting Random WalkersThe collective behavior of self-interacting random walkers (SIRWs)\, also known as trail-interacting particles\, gives rise to new challenges in both physics and mathematics. The shared spatial memory generated through their deposition process leads to complex interactions and emergent phenomena. From previous studies emerge two classes of SIRWs: one in which the interaction with the deposition field saturates (commonly referred to as SATW)\, and another in which the interaction field acts as a potential that grows linearly with deposition (known as TSAW). In this talk\, I will present recent results on systems of N mutually interacting random walkers belonging to these classes. \nBalint Veto: The Brownian web distanceThe random walk web distance is a natural directed distance on the trajectory of coalescing simple random walks. It is given by the minimal number of jumps between different random walk paths when one is only allowed to move forward in time. The Brownian web distance is the scale-invariant limit of the random walk web distance which can be described in terms of the Brownian web. It is integer-valued and has scaling exponents 0:1:2 as compared to 1:2:3 in the KPZ world. The shear limit of the Brownian web distance is still given by the Airy process. A weighted version of the random walk web distance converges to a new explicit distribution that interpolates between the Gaussian and the GUE Tracy-Widom distribution. Based on joint work with Balint Virag. \nRam Adar: Active remodeling in multicellular systemsCells constantly interact with their environment through both mechanical and chemical cues. Migrating cells\, for instance\, induce irreversible local changes in the density and organization of the surrounding extracellular matrix. We refer to this process as “active remodeling”. The remodeled environment biases subsequent cellular motion and can generate new forms of collective organization and dynamics. From a theoretical perspective\, this behavior can be described by the coupled dynamics of two fields: an active field undergoing reaction-diffusion dynamics\, and an environmental field that is locally enslaved to the active field. We will illustrate this framework in two settings. First\, we will show how active remodeling alters the emergence of nematic order in active systems\, motivated by extracellular matrix remodeling by fibroblast cells. Second\, we will show how the degradation of a confining environment leads to subdiffusive dynamics and may account for the expansion rate of cancer spheroids.
URL:https://www.math.ens.psl.eu/evenement/recent-progress-on-self-interacting-processes-and-non-reversible-monte-carlo/
LOCATION:Salle W (ENS)
CATEGORIES:Programme SP(A)M!
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260519T093000
DTEND;TZID=Europe/Paris:20260519T123000
DTSTAMP:20260608T155700
CREATED:20251018T115511Z
LAST-MODIFIED:20260511T081952Z
UID:20144-1779183000-1779193800@www.math.ens.psl.eu
SUMMARY:Vlad Vicol - On self-similar blowup in 3D incompressible fluids
DESCRIPTION:We discuss constraints on hypothetical finite-time (backwards) self-similar blow-up solutions for solutions of incompressible Euler and incompressible Navier-Stokes on R^3. In various situations\, we show that the very existence of a smooth similarity profile imposes strong restrictions on the similarity exponent. We also discuss new Liouville-type theorems for the viscous problem.
URL:https://www.math.ens.psl.eu/evenement/vlad-vicol/
LOCATION:Jussieu —  salle 15-16-309\, 4 Place Jussieu\, Paris\, 75005\, France
CATEGORIES:Séminaire Analyse non linéaire et EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260520T131500
DTEND;TZID=Europe/Paris:20260520T141500
DTSTAMP:20260608T155700
CREATED:20260401T122300Z
LAST-MODIFIED:20260518T081746Z
UID:21207-1779282900-1779286500@www.math.ens.psl.eu
SUMMARY:Rémi Coulon - Les géométries de Thurston : un peu d'illustration au service de la recherche
DESCRIPTION:Le théorème de géométrisation est un achèvement mathématique majeur du début du XXIème siècle. Il stipule\, grosso modo\, que toute variété topologique de dimension trois\, peut être comprise au moyen de huit géométries modèles\, appelées géométries de Thurston. Certaines d’entres elles sont familières des mathématiciennes et mathématiciens : la géométrie sphérique\, euclidienne\, ou hyperbolique. D’autres sont un plus étranges comme Nil ou Sol. Dans cet exposé on présentera un projet de visualisation (dans le prolongement des travaux de Pierre Berger) : que verrait-on si nous vivions dans l’une de ces géométries ? Au cours de cette promenade mathématique\, on verra comment la réalisation d’illustrations vient mettre à l’épreuve nos connaissances\, apporte un point de vue nouveau sur des sujets parfois anciens et soulève de nouvelles questions de recherche. \n\n\n\n\n\n\n\nSéminaires des Mathématiques
URL:https://www.math.ens.psl.eu/evenement/remi-coulon/
LOCATION:ENS — amphi Galois\, 45 rue d'Ulm\, Paris\, France
CATEGORIES:ANNÉE 2025-2026,Prochaine séance,Séminaire Des mathématiques
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260526T170000
DTEND;TZID=Europe/Paris:20260526T180000
DTSTAMP:20260608T155700
CREATED:20260518T082317Z
LAST-MODIFIED:20260518T112043Z
UID:21743-1779814800-1779818400@www.math.ens.psl.eu
SUMMARY:Quelques modèles de dynamique des populations: limites d'échelles
DESCRIPTION:Nous commencerons par introduire la notion de processus de Markov à sauts qui généralise les chaînes de Markov aux temps continus. Lorsque ces processus sont à valeurs vectorielles\, ils peuvent être réécrits sous forme d’équation différentielle stochastique. Ensuite\, le modèle logistique de Verlhust sera dérivé en tant que limite en grande population de ces modèles stochastiques. Dans le cas de populations évoluant sur un maillage discret\, la méthode permet de dériver des EDP de réaction-diffusion en faisant tendre la taille de la maille vers zéro ainsi que le nombre d’individus par maille vers l’infini. Enfin\, en étudiant le cas des processus de contact il est possible de dériver plus naturellement que dans les approches précédentes la notion de capacité de charge de l’environnement tout en se passant de l’hypothèse d’un grand nombre d’individus par maille. \n\n\n\n.
URL:https://www.math.ens.psl.eu/evenement/quelques-modeles-de-dynamique-des-populations-limites-dechelles/
LOCATION:Salle W
CATEGORIES:Colloquium doctorant
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260529T110000
DTEND;TZID=Europe/Paris:20260529T120000
DTSTAMP:20260608T155700
CREATED:20260507T080030Z
LAST-MODIFIED:20260507T080031Z
UID:21694-1780052400-1780056000@www.math.ens.psl.eu
SUMMARY:Automath! Léo Dreyfus-Schmidt: AI tools for the working mathematician
DESCRIPTION:Recent AI systems are increasingly entering the working environment of mathematicians\, offering new ways to explore ideas\, search the literature\, and formalize arguments. In this talk\, we will present a selection of such tools\, focusing on their practical use in everyday mathematical work.
URL:https://www.math.ens.psl.eu/evenement/automath-leo-dreyfus-schmidt-ai-tools-for-the-working-mathematician/
LOCATION:campus de Jussieu (amphi 15)
CATEGORIES:Séminaire Automath
END:VEVENT
END:VCALENDAR