The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars  [Next 30 ]  
[ scheduler view ] 
Monday 27 March 2023, 10:45 at LPTMC, campus Jussieu, couloir 1213, 5ème, salle 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  Walking drops on Faraday waves are one of the rare examples of nonquantum waveparticle duality. A series of striking experiments with one walking drop has led to behaviors that were thought to be the peculiar to the quantum scale. I will present a recent numerical and experimental investigation involving the coupling of two walking drops. To our great surprise, we found that the statistical behavior of this system shares some nonexpected features of collective emission of photons in quantum optics, including superradiance and violation of Bell's inequality. This result is very intriguing as the quantum counterpart is the signature of nonseparable states which in our case, is the result of a collective wave selforganization. 
Monday 27 March 2023, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  J'expliquerai le lien entre pavages par dominos et suites de partitions, une idÃ©e dÃ©veloppÃ©e entre autres en collaboration avec JÃ©rÃ©mie Bouttier. Je montrerai comment on peut rajouter une condition "symplectique" sur ces suites de partitions et dÃ©finirai les pavages du triangle Aztec gÃ©nÃ©ralisÃ©. Pour certaines formes on retrouve le triangle Aztec dÃ©fini par Philippe Di Francesco. Dans certains cas on montre que le nombre de pavages a une jolie formule produit. Travail en collaboration avec Freddie Huang et Christian Krattenthaler. [The talk will be in English unless all the audience is comfortable with French. It will also be streamed online, please ask the organizers for the link.] 
Tuesday 28 March 2023, 14:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite seminar + zoom. For zoom info, please write to valentina.ros@universiteparissaclay.fr or check LPTMS website )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 



Abstract:  The characterization of the structure of the manifold of lowenergy lying states in neural networks is among the most fundamental theoretical questions in machine learning. In recent years, many empirical studies on the landscape of neural networks and constraint satisfaction problem have shown that the lowlying configurations are often found in complex connected structures, where zeroenergy paths between pairs of distant solutions can be constructed. In this talk, I will discuss the geometrical organization and the connectivity properties of solutions in two linear neural network models having respectively binary and continuous weights: the "binary'' and the" negative perceptron''. I will show that wide flat minima arise as complex extensive structures from the coalescence of minima around "highmargin'' (i.e. locally robust) configurations [1]. Moreover, I will introduce a novel analytical method for characterizing the typical energy barriers between groups of configurations sampled from the zerotemperature measure of the problem [2]. In the negative perceptron case, we find that, despite the overall nonconvexity of the space of solutions, below a critical fraction of constraints $\alpha_\star$ the geodesic path between any solution and the robust solutions of the problem, located in the interior of the solution space, remains strictly zeroenergy. The value of $\alpha_\star$ where this simple connectivity property breaks down is compatible with the point at which the dense core of solutions fragments in multiple smaller pieces [3]. References: [1] C. Baldassi, C. Lauditi, E. M. Malatesta, G. Perugini, and R. Zecchina, Physical Review Letters 127, 278301 (2021). [2] B. L. Annesi, C. Lauditi, C. Lucibello, E. M. Malatesta, G. Perugini, F. Pittorino, and L. Saglietti, In preparation (2023). [3] C. Baldassi, E. M. Malatesta, G. Perugini, and R. Zecchina, In preparation (2023). 
Tuesday 28 March 2023, 14:45 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  In this talk, I will review the (boostless) cosmological bootstrap approach to the study of cosmological correlators from inflation, in which symmetries and general physical principles such as causality, unitarity and locality substitute the traditional modelbuilding and lead to a variety of general results and new predictions for primordial signals. The object of study is the field theoretic wavefunction and its wavefunctions coefficients, from which all correlators can be (perturbatively) derived. Wavefunction coefficients are the close analog of amplitudes in flat space and many results for amplitudes have avatars in the cosmological bootstrap. In the first part of the talk, I will review a few core results: (i) Causality implies that "offshell" wavefunction coefficients (a.k.a. cosmological "inout" Green's function) are analytic functions of offshell energies (nonperturbatively) in the lowerhalf complex plane, whose singularity on the negative real axis are classified. (ii) Unitarity implies an infinite set of relations between higher and lower order contributions in perturbation theory known collectively as the cosmological optical theorem. (iii) Manifest locality constrains wavefunction coefficients in the form of analyticallycontinued soft limits. In the second part of the talk, I discuss four phenomenological results recently derived with these techniques: (1) The treelevel scalar bispectrum to all orders in derivatives both assuming scale invariant and oscillations (resonant nonGaussianity) 
Wednesday 29 March 2023, 13:30 at DPTPHYSENS, ConfIV (E244)  24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  Understanding the emergence of the rules of statistical mechanics for an isolated manybody system from an underlying quantummechanical microdynamics is a longstanding problem of fundamental physics. Concepts from the theory of quantized classically chaotic systems can be used to resolve at least some of the key issues, and lead to the notion of “eigenstate thermalization”: individual energy eigenstates of the system as a whole appear to be states of thermal equilibrium when probed by local (fewbody) observables. 
Wednesday 29 March 2023, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  Infinite distance limits in families of quantum theories are observed to enjoy a number of seemingly universal properties: they have "logarithmic" metric singularities, are always associated with weakcoupling limits, andin quantum gravitational theoriesare tied to the appearance of a tower of exponentially light fields. The goal of this talk is to explain why, and the extent to which, these features are universal. By using informationtheoretic tools, I will explain how the first two properties are consequences of unitarity: it dictates that, in these limits, there must be observables that factorize and the metric must have a logarithmic singularity. I will also explain why these limits necessarily have such dramatic behavior in quantum gravitational theories. Since gravity universally couples to stress energy, it presents a fundamental obstacle to factorization and must decouple in any consistent factorization limit. I will explain how this perspective provides a bottomup motivation for the Swampland Distance Conjecture and points towards ways around it. 
Wednesday 29 March 2023, 16:00 at
IHES,
Centre de conférences Marilyn et James Simons ( + d'infos : https://indico.math.cnrs.fr/event/9621/ )  PTIHES (Séminaire de physique théorique de l'IHES)  condmathepthquantph 



Abstract:  The presence of nearby conformal field theories (CFTs) hidden in the complex plane of the tuning parameter was recently proposed as an elegant explanation for the ubiquity of "weakly firstorder" transitions in condensed matter and highenergy systems. In this work, we perform an exact microscopic study of such a complex CFT (CCFT) in the twodimensional O(n) loop model. The wellknown absence of symmetrybreaking of the O(n>2) model is understood as arising from the displacement of the nontrivial fixed points into the complex temperature plane. Thanks to a numerical finitesize study of the transfer matrix, we confirm the presence of a CCFT in the complex plane and extract the real and imaginary parts of the central charge and scaling dimensions. By comparing those with the analytic continuation of predictions from Coulomb gas techniques, we determine the range of validity of the analytic continuation to extend up to ng≈12.34, beyond which the CCFT gives way to a gapped state. Finally, we propose a beta function which reproduces the main features of the phase diagram and which suggests an interpretation of the CCFT as a liquidgas critical point at the end of a firstorder transition line. 
Thursday 30 March 2023, 09:00 at LPTMS, Petit amphi, bâtiment Pascal n° 530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Friday 31 March 2023, 09:00 at LPTMS, Petit amphi, bâtiment Pascal n° 530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Friday 31 March 2023, 10:15 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  This course will provide a modern point of view on the wide world of large $N$ conformal field theory (CFT) in diverse spacetime dimensions, placed in the context of the conformal bootstrap and the AdS/CFT Correspondence.\\ Some questions we will tackle: \\ What is a ``Holographic CFT''? \\  When does a CFT give rise to an equivalent, emergent simple gravity description? \\  What is the conformal bootstrap, and how is it used to constrain and classify the space of consistent large $N$ CFTs and theories of quantum gravity? \\  Is string theory the only choice? How can we detect strings and extra dimensions from properties of field theories? \\  What precise predictions does quantum gravity seem to make about the space of strongly coupled CFTs? \\ Provisional lecture plan: \\ Lectures III: Introducing CFTs and their data, large $N$ conformal bootstrap, AdS/CFT, and the notion of ``Holographic CFT'' \\ Lecture III: Correlation functions and holography \\ Lecture IV: Bootstrapping the space of Holographic CFTs \\ Lecture V: Special focus: Twodimensional CFTs and AdS$_3$ gravity \\ \\ Course website: https://courses.ipht.fr/?q=en/node/310 \\ \\ Videoconference and in person in Salle Itzykson, IPhT \\ Livestream on youtube.com/IPhTTV: no subscription required 
Monday 3 April 2023, 13:30 at LPENS, Salle Froidevaux (Département de géosciences de l'ENS)  LPENSMDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)  condmat 



Abstract:  In the context of photonic quantum information science, the 2D material hexagonal boron nitride (hBN) has emerged as a very promising material, allowing realisation of compact heterostructures and integrated photonic devices. Moreover, this widegap material hosts singlephoton emitters with advantageous optical properties. However, these deep defects initially suffered from random emission wavelength and spatial location, thereby limiting their scalability for practical applications. We have recently demonstrated a technique to generate quantum emitters in hBN with controlled position and wavelength. The emitters are locally activated in exfoliated hBN single crystals using a focused electron beam, opening the way for topdown integration in nanostructures. They exhibit bright and narrow lines with high optical coherence and low ensemble distribution. I will present their fabrication technique, their optical properties and coherent control, as well as a twophoton interference experiment to evaluate their indistinguishability. I will also show recent results of deterministic integration into photonic structures. Altogether, the controlled generation of coherent quantum emitters in 2D materials open appealing perspectives in quantum photonics. 
Monday 3 April 2023, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Property (T) is a fundamental notion introduced by D. Kazhdan in the mid 1960's, that found numerous applications since then, notably in the context of rigidity of group actions. For a group G generated by a finite set S, property (T) means that there is a constant K>0 such that given any unitary representation of G on a Hilbert space without nonzero invariant vectors, every unit vector is displaced by some element of S to a point that is at least K apart. Finite groups have that property. Kazhdan proved that lattices in simple Lie groups of rank at least 2 all do as well. I will introduce a new class of infinite groups enjoying Kazhdan's property (T) and admitting alternating group quotients of arbitrarily large degree. Those groups are constructed as automorphism groups of the ring of polynomials in n indeterminates with coefficients in the finite field of order p, generated by a suitable finite set of polynomial transvections. As an application, we obtain explicit presentations of hyperbolic Kazhdan groups with infinitely many alternating group quotients, and explicit generating pairs of alternating groups of unbounded degree giving rise to expander Cayley graphs. The talk is based on joint work with Martin Kassabov. 
Monday 3 April 2023, 14:30 at
IAP,
Planétarium de la Cité des Sciences ( If you plan to attend, please register by email to seminaire.iap.planetarium@iap.fr preferably before March 25. )  SEMEXCEP (Séminaire exceptionel)  grqchepthphysics 



Abstract:  Most relativistic effects, whether due to special relativity (aberration, Doppler effect) or general relativity (distortion of light) have been extensively documented for decades. On the other hand, the works on visualization of these and the attempts to render them as realistically as possible are less common. Given the fact that they occur with an intensity that is sometimes highly variable depending on the direction of observation, their simulation is particularly suitable for a hemispherical projection such as that offered by a digital planetarium. In addition, some effects still remain poorly documented, such as the visual translation of extreme tidal effects within a black hole, or the crossing of a wormhole. Taking advantage of the immersive environment offered by the planetarium of the Cité des Sciences, I will present in this seminar a set of relativistic effects of increasing complexity as they would be perceived by an observer located close to, or even inside various types of black holes. 
Monday 3 April 2023, 16:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Dirichlet's theorem in Diophantine approximation implies that for any real x, there exists a rational p/q arbitrarily close to x such that $xp/q < 1/q^2$. In addition, the exponent 2 that appears in this inequality is optimal, as seen for example by taking $x=\sqrt2$. In 1967, Wolfgang Schmidt suggested a similar problem, where x is a real subspace of $R^d$ of dimension $\ell$, which one seeks to approximate by a rational subspace v. Our goal will be to obtain the optimal value of the exponent in the analogue of Dirichlet's theorem within this framework. The proof is based on a study of diagonal orbits in the space of lattices in $R^d$. 
Tuesday 4 April 2023, 11:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite seminar + zoom. For zoom, please write to valentina.ros@universiteparissaclay.fr or check http://lptms.upsud.fr/fr/activites/seminaires/ )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Tuesday 4 April 2023, 14:00 at
LPTHE,
library & Zoom link in comments ( Join Zoom Meeting https://cern.zoom.us/j/63419535770?pwd=WlpoNnF1M2xOY2cyM0tzSXZCdWFtQT09 Meeting ID: 634 1953 5770 Passcode: 387151 )  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  It is wellknown that perturbative expansions of QFT observable suffer from infrared (IR) divergences both in the phasespace of realemission contributions and in the loop amplitudes of virtual contributions. Traditionally, the two are handled separately through a combination of local subtraction counterterm and dimensional regulation. Local Unitarity is an alternative formulation using the LoopTree Duality (LTD) theorem and where the Kinoshita–Lee–Nauenberg (KLN) cancellation pattern is leveraged to achieve a direct cancellation of realemission and loop IR divergences at the local level. Together with an automated local renormalization procedure based on the Roperation, the resulting expression is locally finite and thus amenable to numerical integration at arbitrary perturbative orders and for processes with finalstate singularities only. I will present an overview of the various ingredients entering that construction and the challenges awaiting my new group at the University of Bern. 
Wednesday 5 April 2023, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We review recent progress in understanding the resurgent properties of integrable field theories in two dimensions. After a brief recap on elementary notions about Borel resummations, we start with a quick historical detour on the study of the large order behaviour of perturbation theory in quantum field theory (QFT) before the advent of resurgence. We then introduce basic notions of resurgence and apply it on three wellknown integrable field theories which are UVfree, develop a mass gap in the IR, admit a 1/N expansion, and present the so called renormalon singularities. The interplay between resurgent properties and the 1/N expansion is discussed. The observable of interest is the free energy in the presence of a chemical potential coupled to a conserved charge, which can be computed exactly with thermodynamic Bethe ansatz techniques and/or large N QFT methods. Results at finite N will also be reviewed. 
Wednesday 5 April 2023, 14:00 at LPENS, L357  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  Understanding the collective motion of selfpropelling particles, such as flocking birds, is a problem that is almost 30 years old but remains topical. Considering minimal flocking models (the Vicsek model and its variants) I will present several results that tend to show the fragility of the polar ordered phases of collective motion. First, any amount of spatial anisotropy destroys the longrange correlations and giant density fluctuations of these states. Then, the ordered state of the "Malthusian" model, with population dynamics, is unstable to the nucleation of topological defect as well as the ordered state in the Active Ising model that has discrete symmetry. 
Thursday 6 April 2023, 10:00 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  The locality in space of interactions between elementary particles is a key property of our universe. This locality is hardwired into quantum field theoretic descriptions of nature. However, locality and indeed space itself are likely not fundamental concepts. In holographic duality, local interactions on a dynamical spacetime emerge from "large N" matrices where no locality is manifest in the microscopic Hamiltonian. The emergence of locality from matrix theories is wellestablished but not wellunderstood. In recent years it has been appreciated that locality is closely tied up with socalled “area law” entanglement of the microscopic degrees of freedom. I will discuss a particularly robust notion of entanglement in matrix theories that is rooted in an underlying Gauss law constraint and show how simple models of matrix, or ‘fuzzy' geometry contain area law entanglement. 
Thursday 6 April 2023, 11:45 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will discuss the low energy dynamics of systems which are close to a superfluid phase transition. In addition to the hydrodynamics of conserved quantities and the Goldstone mode, the amplitude of the order parameter needs to be included in the description. After presenting a field theoretic construction of a suitable effective theory, I will examine the phenomenology of suitable holographic systems. 
Thursday 6 April 2023, 14:00 at LPTHE, En visio (zoom link to be given)  TQM (Theory of quantum matter)  condmat 



Abstract:  TBA 
Thursday 6 April 2023, 14:00 at LPTM, 4.13b + Teams distanciel  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  physics.histph 



Abstract:  On date habituellement la naissance de la Mécanique Quantique au 14 décembre 1900. Ce jourlà, Max Planck propose devant la société Allemande de Physique une solution pour décrire la distribution spectrale du rayonnement électromagnétique piégé dans une enceinte à l’équilibre à une température fixée. L’application des méthodes récentes de la Physique Statistique de MaxwellBoltzmann à ce problème dit du ‘’corps noir’’ aboutissait à des impasses, incompatibles avec la Physique classique et la théorie triomphante de l’électromagnétisme de Maxwell. L’’’acte de désespoir’’ proposé par Planck est le début d’une extraordinaire aventure intellectuelle dont Einstein sera le véritable initiateur à partir de 1905. Dans cet exposé, je passerai en revue quelquesunes des étapes de cette nouvelle construction intellectuelle, le lent murissement des idées qui a conduit aux premières hypothèses de Planck, l’importance des méthodes de la Physique Statistique, la notion de quantum de lumière que l‘on appellera plus tard le photon, la dualité OndeCorpuscule pour la lumière en 1909, les difficiles discussions du fameux congrès Solvay de 1911 réunissant tous les grands scientifiques de l’époque, jusqu’à la proposition par Einstein que les particules de matière soient aussi des ondes, quasiment en même temps que Louis de Broglie en 1924. 
Tuesday 11 April 2023, 11:00 at IPHT, Amphi Claude Bloch, Bât. 774  IPHTGEN (Séminaire général du SPhT)  physics 


Tuesday 11 April 2023, 11:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite + zoom. For zoom info, please write to valentina.ros@universiteparissaclay.fr or check http://lptms.upsud.fr/en/activites/seminaires/ )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Tuesday 11 April 2023, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire de MathématiqueBiologie )  MATHIHES (TBA)  math 



Abstract:  Though proteins are basic blocks of life, mathematicians are only starting to formalize the fundamental concepts of structural biology. The key missing piece was the definition of a practical equivalence on (tertiary structures of) proteins embedded in 3dimensional space. Since protein structures are determined in a rigid form, the strongest equivalence in practice is rigid motion or isometry also including reflections. We can consider a protein an ordered sequence of ordered alphacarbons (protein backbone) or a cloud of unlabeled atomic centers, which allows us to compare any molecules under isometry. The pairwise comparisons of all protein chains in the Protein Data Bank (PDB) by complete isometry invariants unexpectedly detected thousands of pairs that have identical coordinates of all alphacarbon atoms (often all atoms as well). More than 325 billion pairwise comparisons were completed in less than two days on a modest desktop, implemented by Alexey Gorelov in our joint work. Some pairs of chains differ in primary sequences of their amino acids, which seems physically impossible. We discussed the findings with the PDB validation team and several authors confirmed that corrections in the PDB are needed. Using more flexible isometry invariants for rigid clouds of unlabeled atomic centers, we produced a continuous map revealing hot spots in the whole PDB. 
Wednesday 12 April 2023, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We review recent progress in understanding the resurgent properties of integrable field theories in two dimensions. After a brief recap on elementary notions about Borel resummations, we start with a quick historical detour on the study of the large order behaviour of perturbation theory in quantum field theory (QFT) before the advent of resurgence. We then introduce basic notions of resurgence and apply it on three wellknown integrable field theories which are UVfree, develop a mass gap in the IR, admit a 1/N expansion, and present the so called renormalon singularities. The interplay between resurgent properties and the 1/N expansion is discussed. The observable of interest is the free energy in the presence of a chemical potential coupled to a conserved charge, which can be computed exactly with thermodynamic Bethe ansatz techniques and/or large N QFT methods. Results at finite N will also be reviewed. 
Wednesday 12 April 2023, 14:00 at LPENS, L357  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  TBA 
Wednesday 12 April 2023, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  TBD 
Thursday 13 April 2023, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Thursday 13 April 2023, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  We give a purely topological formula for the square class of the central value of the Lfunction of a symplectic representation on a curve. We also formulate a topological analogue of the statement, in which the central value of the Lfunction is replaced by Reidemeister torsion of 3manifolds. This is related to the theory of epsilon factors in number theory and Meyer's signature formula in topology among other topics. We will present some of these ideas and sketch aspects of the proof. This is joint work with Akshay Venkatesh. 

[ English version ] 