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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 May 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 | IPHT-PHM (Séminaire de physique mathématique) | math-ph |
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| Abstract: | Indirect measurements in quantum mechanics lead to stochastic evolution equations for the density matrix, the so-called quantum trajectories. \par Generically, the measurements themselves favor wave function collapse towards certain states, while the internal evolution, if it does not preserve these states, prevents the collapse. In this talk I'll describe the regime when the time scale of the collapse is very short compared to the typical time scale of the internal evolution. In this regime, which is a strong noise regime, quantum trajectories, though continuous, are closely related to Poisson processes and a strong universality emerges. \par The mathematical tools we use have recently attracted the attention of probabilists who are now aiming at a fully rigorous treatment. | |
| Monday 27 May 2019, 13:30 at LPENS, Conf IV | LPA (Séminaire du laboratoire Pierre Aigrain) | cond-mat |
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| Tuesday 28 May 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 | IPHT-GEN (Séminaire général du SPhT) | physics |
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| Abstract: | Synapses are important biological structures that serve to transmit information between neurons and are thought to be the sites of learning and memory. Yet, it has remained enigmatic how memory can be retained for years while synaptic components turnover over the course of hours. Similarly, when learning a complex task, the received feedback seems most often global and poorly informative. It is then quite unclear how it can serve to properly adjust the strengths of numerous different synapses, the so-called ``credit-assignment problem''. After recalling some elements of synapse biophysics and some relevant experimental findings, I will discuss our recent work in collaboration with the teams of A Triller and B Barbour at IBENS, aiming at addressing these two puzzles. | |
| Tuesday 28 May 2019, 14:00 at APC, 646A - Mondrian | APC-TH (Seminar of the theory group of APC) | gr-qc |
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| Abstract: | Until now, observations and experiments have confirmed General Relativity (GR) as the best theory of gravity. The current gravitational wave interferometers, LIGO and Virgo, as well as the future space-based detector LISA, will permit to challenge further GR in the highly dynamical and strong field regime of gravity. In this talk, I will focus on alternative theories with an additional scalar degree of freedom, in relation to compact objects. In particular, I will describe the evolution of compact binary systems in these theories using the post-Newtonian formalism. I will show that one of the most interesting phenomenological consequence lies in finite-size effects. | |
| Tuesday 28 May 2019, 17:15 at LPENS, Salle Jaures | COLLOQUIUM-ENS (Colloquium of the Physics Department of ENS) | hep-th |
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| Wednesday 29 May 2019, 11:30 at
IPN,
Bâtiment 100, Salle A015 ( $ $ ) | IPN-THEO (Séminaire du groupe de physique théorique de l'IPN Orsay) | nucl-th |
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| Abstract: | In this talk I will show how an Effective Field Theory for weakly-bound few-body systems ("Halo EFT") aids the modeling and understanding of light nuclei in the $p$-shell. After introducing Halo EFT I will discuss two examples of its use. First, I will describe our recent analysis of the reaction $^3$He($\alpha$, $\gamma$)~[1]. In this case we take $^3$He and $^4$He as the effective degrees of freedom and work to next-to-leading order in the EFT. We use a Bayesian analysis to perform the extrapolation of higher-energy data to solar energies and find a markedly smaller uncertainty to previous evaluations, as well as significant constraints on $^3$He-$^4$He scattering parameters. Second, I will demonstrate that a three-body ($\alpha$-neutron-proton) model of $^6$Li exhibits a correlation between the deuteron-$\alpha$ scattering length and the $^6$Li binding energy~[2]. Such correlations appear generically in three-body systems with weak binding (cf. the Phillips line in the $A=3$ system) and can be understood as a consequence of the requirement that the EFT be renormalized. The emergence of such a correlation in the presence of $p$-wave nucleon-$\alpha$ interactions is particularly striking, as is the fact that it is rather insensitive to the actual values of the $p$-wave phase shifts. I will close by discussing the implications of this finding for model and EFT treatments of $^6$He and $^6$Li. | |
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| Wednesday 29 May 2019, 14:30 at
IPN,
Bâtiment 100, Salle A015 ( $ $ ) | IPN-THEO (Séminaire du groupe de physique théorique de l'IPN Orsay) | nucl-th |
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| Abstract: | The main goal of the Continuum Discretized Coupled Channel (CDCC) method is to solve the Schrödinger equation for reactions where the projectile presents a cluster structure, and a low dissociation energy. The CDCC method has been introduced forty years ago to describe deuteron induced reactions. Owing to the low binding energy of the deuteron, it was shown that including continuum channels significantly improves the description of d$+$nucleus elastic cross sections. The simplest variant of CDCC describes scattering of a two-body nucleus with a structureless target, but extensions to three-body projectiles have been performed recently. The projectile continuum is approximated by a finite number of square-integrable states, up to a given truncation energy. I present here a new development of the CDCC method, which aims at describing reactions where the projectile and the target have a low separation energy. This leads to four-body (or more) calculations.I solve the coupled-channel system by using the $R$-matrix method on a Lagrange mesh. Applications to $^{11}$Be$+$d and $^7$Li$+$d scattering are presented. | |
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| Monday 3 June 2019, 10:00 at LPTENS, L357/359 | WORK-CONF (Workshop or Conference) | hep-th |
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| Monday 3 June 2019, 10:45 at LPTMC, Jussieu, tower 13-12, room 5-23 | SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) | cond-mat.mes-hall |
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| Abstract: | Single-file transport, arising in quasi-one-dimensional geometries where particles cannot pass each other, is characterized by the anomalous dynamics of a probe, notably its response to an external force. I will present a simple hydrodynamic framework that allows to compute this response, and also the response of several probes to arbitrary external forces, where an unbinding transition can occur. | |
| Monday 3 June 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 | IPHT-PHM (Séminaire de physique mathématique) | math-ph |
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| Abstract: | In this talk I will first sketch the derivation of LIA (Local Induction Approximation) as a model for the dynamics of vortex filaments in 3-D fluids. Then I will describe its link with the classical continuous Heisenberg model and with the 1-D cubic Schrödinger equation. Finally I shall present some recent results on solutions generating a singularity in finite time. | |
| Tuesday 4 June 2019, 10:00 at IHP, Amphitheatre Hermite | WORK-CONF (Workshop or Conference) | hep-th |
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| Tuesday 4 June 2019, 14:00 at APC, 646A - Mondrian | APC-TH (Seminar of the theory group of APC) | gr-qc |
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| Tuesday 4 June 2019, 14:00 at
LPTM,
4.13 St Martin II ( Ref: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.109.268101 ) | SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) | CoRR.LG |
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| Abstract: | In this talk, provided a streamlined introduction to statistical learning and related information retrieval achieved by associative neural networks, I will deepen some recent progresses via their statistical mechanical formalization. I will focus on the nature of the information to store (i.e. analog vs digital patterns) and on the role of dilution in the underlying graphs where the neurons are hosted (particularly relating network 's dilution to spontaneous multi-tasking capabilities the net experiences as a whole). Finally, I will discuss how by 'letting these machines sleep' it is possible to sensibly increase their performances, much as their real (i.e. biological) counterparts. | |
| Wednesday 5 June 2019, 09:00 at IPHT, Amphi Claude Bloch, Bât. 774 | WORK-CONF (Workshop or Conference) | physics |
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| Abstract: | \noindent The Itzykson Meeting is held every year in Saclay to honour the memory of Claude Itzykson. \medskip \par Effective field theory is one of the deepest and most useful guiding principles in physics. Its tools and methods allow one to study the universal aspects of entire classes of unknown microscopic models, with their main features being captured by symmetries and few relevant parameters of the effective degrees of freedom. Because of its universality, it finds applications across all scale in physics: from super-Hubble scales all the way to the Planck length. It is successfully applied to cosmology to describe the early cosmic inflation, the current cosmic acceleration, the dynamics of the large scale structure and the dark matter. Its methods have found recent applications in the theory of gravitational wave emission by binary inspirals, and in the new multimessanger astrophysics: new and conceptually compelling ways to perform calculations and predictions are being developed by making contact with the methods of scattering amplitudes of particle physicists. \par One of the goals of the conference is to bring together experts working with Effective Field Theories in all these fields, in order to exchange ideas and foster new insights and techniques. \medskip \\ Website: https://indico.in2p3.fr/event/18200/ \\ Scient. Organisers: Brando Bellazzini, John Joseph Carrasco and Filippo Vernizzi. \\ The workshops is supported by the Programmes Nationaux GRAM and PNCG of CNRS/INSU with INP and IN2P3 cofunded by CEA and CNES, by the IPhT of CEA-Saclay, by the Université Paris-Saclay, and by P2IO. | |
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| Wednesday 5 June 2019, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique Paris-Pékin-Tokyo ) | MATH-IHES (TBA) | math |
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| Abstract: | Let p be a rational prime, q>1 a p-power and P a non-constant irreducible polynomial in F_q[t]. The notion of Drinfeld modular form is an analogue over F_q(t) of that of elliptic modular form. Numerical computations suggest that Drinfeld modular forms enjoy some P-adic structures comparable to the elliptic analogue, while at present their P-adic properties are less well understood than the p-adic elliptic case. In 1990s, Taguchi established duality theories for Drinfeld modules and also for a certain class of finite flat group schemes called finite $\nu$-modules. Using the duality for the latter, we can define a function field analogue of the Hodge-Tate map. In this talk, I will explain how the Taguchi's theory and our Hodge-Tate map yield results on Drinfeld modular forms which are classical to elliptic modular forms e.g. P-adic congruences of Fourier coefficients imply p-adic congruences of weights. | |
| Friday 7 June 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/228 ) | COURS (Cours) | cond-mat|hep-th|physics|quant-ph |
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| Abstract: | \noindent Modern computers have a growing number of processors or ``cores''. From a few units in a simple laptop, to several thousands in big servers, their number has been growing quickly over the years. But to fully take advantage of this computing power, it is necessary to have codes or softwares being able to distribute a given task over several processors working in parallel. \\ \\ These lectures will present an introduction to parallel programming in the context of scientific calculations; \par Introduction to hardware aspects (``shared'' versus ``distributed'' memory, communication between processors, vectorization, etc.) \par Solutions based on ``already-parallel'' softwares (from linear algebra libraries to highlevel computer algebra softwares) \\ \\ We will then present two widely used libraries for code parallelization, OpenMP (Open MultiProcessing) and MPI (Message Passing Interface). \\ \\ These lectures will be based on simple and concrete examples. They are intended for people with some basic programming knowledge (for instance in C/C++, Python or Fortran), but no prior experience with parallelization. | |
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| Friday 7 June 2019, 14:00 at APC, Amphitheatre Pierre Gilles de Gennes | APC-COLLOQUIUM (Colloquium de l'APC) | astro-ph |
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| Friday 7 June 2019, 14:00 at LPTHE, library | LPTHE-PPH (Particle Physics at LPTHE) | hep-ph |
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| Abstract: | Some dark matter scenarios will be discussed, which call for new paradigms for collider searches as well as indirect signals from the outer space. The two examples pointed out are (a) a non-thermal dark matter particle with ultra-feeble interaction with the rest of the spectrum, and (b) a WIMP with trans-TeV mass. The first scenario may open up new strategies at the LHC, while the usefulness of radio signals from dwarf galaxies is pointed out for the second. | |
| Tuesday 11 June 2019, 14:00 at APC, 646A - Mondrian | APC-TH (Seminar of the theory group of APC) | gr-qc |
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| Tuesday 11 June 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets ) | MATH-IHES (TBA) | math |
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| Abstract: | : I will give a formula for the Masur-Veech volume of the moduli space of quadratic differentials in terms of psi-classes (in the spirit of Mirzakhani's formula for the Weil-Peterson volume of the moduli space of hyperbolic surfaces). I will also show that Mirzakhani's frequencies of simple closed hyperbolic geodesics of different combinatorial types coincide with the frequencies of the corresponding square-tiled surfaces. I will conclude with a (mostly conjectural) description of the geometry of a "random" square-tiled surface of large genus and of a "random" multicurve on a topological surface of large genus. The talk is based on joint work in progress with V. Delecroix, E. Goujard and P. Zograf. It is aimed at a broad audience, so I will try to include all necessary background. | |
| Tuesday 11 June 2019, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets ) | MATH-IHES (TBA) | math |
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| Abstract: | We consider discrete groups admitting proper cocompact topological actions by homeomorphisms on R^4. We will say that such a group Γ is geometrized if we can build an action of Γ by projective transformations on a properly convex open subset of the real projective 4-space, or a convex cocompact action of Γ on the real hyperbolic 5-space or on its Lorentzian counterpart, the anti-de Sitter 5-space. Certain uniform lattices of the isometry group of hyperbolic 4-space are geometrizable by the three geometries mentioned above. We will discuss the existence of groups which are not uniform lattices in hyperbolic 4-space, and which yet admit several of these three geometries. If time allows, we will also discuss the corresponding deformation spaces. This is joint work with Gye-Seon Lee (Heidelberg). | |
| Tuesday 11 June 2019, 17:15 at LPENS, Salle Jaures | COLLOQUIUM-ENS (Colloquium of the Physics Department of ENS) | astro-ph |
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| Abstract: | Since the numerical simulations of the past decades, we now know that the motion of the solar system is chaotic with an exponential divergence increasing the uncertainty in the computations by a factor of 10 every 10 millions of years (Ma). Due to the perturbation of the minor planets Ceres and Vesta, the horizon of predictability of the orbital solutions is limited to about 60 Ma, while our latest solutions should be valid over about 50 Ma. These solutions have been used for the time calibration of sedimentary records and the establishment of geological time scales, using the correlation between the computed variation of insolation on Earth and the recorded sedimentary imprint of the resulting climatic variations. I will discuss the possibility to extend these works beyond the horizon of predictability of 60 Ma imposed by the chaotic variations of the orbits. | |
| Wednesday 12 June 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774 | IPHT-MAT (Séminaire de matrices, cordes et géométries aléatoires) | hep-th |
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| Wednesday 12 June 2019, 15:45 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( \\ https://www.ipht.fr/Phocea/Vie\_des\_labos/Seminaires/index.php?id=993878 ) | COURS-IPHT (Cours de l'Institut de Physique Théorique) | hep-th |
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| Abstract: | In the last 10 years, scientists across many fields have converged on Python as the language of choice for scientific applications; in addition to being powerful, expressive, and friendly, Python benefits from a strong ecosystem of open-source users/developers. Furthermore, the notebook interface and file format have emerged as a powerful mode for computational experimentation and for the exchange of reproducibility of studies. \par This course provides an introduction to the core Python language and to the basic ``stack'' of scientific packages. The tentative list of topics, which can later be modified according to interest and progress, is: \\ 1 - Core Python and the Python standard library; using the Jupyter notebook. \\ 2 - Numpy (arrays, broadly construed); Scipy (numerical methods). \\ 3 - Matplotlib (plotting); Pandas (data tables). \\ 4 - Object-oriented and functional Python. \\ 5 - Wrapping C/C++/Fortran; high-performance Python. \\ 6 - Sympy (symbolic calculations). \par This course won't make you into Python experts (you shouldn't expect to learn a language in a few hours!), but it will give you a sense of what is possible, of where to look for things, and of the overall spirit of the language and its community. If you wish to read ahead, here are recommended tutorials: \\ - https://docs.python.org/3/tutorial = the official language tutorial, staid but authoritative \\ - https://github.com/jakevdp/WhirlwindTourOfPython = a quick introduction to the core Python language \\ - https://jakevdp.github.io/PythonDataScienceHandbook = a thorough overview of scientific Python \par The course will consist of interactive, hands-on tutorials, lasting about 90 minues each. You are encouraged to bring your laptop, with a functional Python 3 installation. We recommend the Anaconda Distribution at https://www.anaconda.com/distribution (Python 3.7 version), which comes with all required packages. However, it is also possible to run Jupyter notebooks in the cloud, which you can do for free with a Google account at http://colab.research.google.com. \\ \\ (Organizer: IPhT/Sylvain Ribault) | |
| Thursday 13 June 2019, 10:00 at IHP, 314 | RENC-THEO (Rencontres Théoriciennes) | hep-th |
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| Thursday 13 June 2019, 11:40 at IHP, 314 | RENC-THEO (Rencontres Théoriciennes) | hep-th |
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| Thursday 13 June 2019, 14:00 at LPENS, Conf IV | LPA (Séminaire du laboratoire Pierre Aigrain) | cond-mat |
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| Abstract: | tba | |
| Friday 14 June 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/228 ) | COURS (Cours) | cond-mat|hep-th|physics|quant-ph |
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| Abstract: | \noindent Modern computers have a growing number of processors or ``cores''. From a few units in a simple laptop, to several thousands in big servers, their number has been growing quickly over the years. But to fully take advantage of this computing power, it is necessary to have codes or softwares being able to distribute a given task over several processors working in parallel. \\ \\ These lectures will present an introduction to parallel programming in the context of scientific calculations; \par Introduction to hardware aspects (``shared'' versus ``distributed'' memory, communication between processors, vectorization, etc.) \par Solutions based on ``already-parallel'' softwares (from linear algebra libraries to highlevel computer algebra softwares) \\ \\ We will then present two widely used libraries for code parallelization, OpenMP (Open MultiProcessing) and MPI (Message Passing Interface). \\ \\ These lectures will be based on simple and concrete examples. They are intended for people with some basic programming knowledge (for instance in C/C++, Python or Fortran), but no prior experience with parallelization. | |
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| Friday 14 June 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes | APC-COLLOQUIUM (Colloquium de l'APC) | astro-ph |
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| Friday 14 June 2019, 14:00 at LPTHE, library | LPTHE-PPH (Particle Physics at LPTHE) | hep-ph |
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