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In this talk we will discuss a new geodesic beam approach to understanding eigenfunction concentration. We characterize the features that cause an eigenfunction to saturate the standard supremum bounds in terms of the distribution of $L^{2}$ mass along geodesic tubes emanating from a point. We also show that the phenomena behind extreme supremum norm growth is identical to that underlying extreme growth of eigenfunctions when averaged along submanifolds. Using the description of concentration, we obtain quantitative improvements on the known bounds in a wide variety of settings.
In this talk we will discuss a new geodesic beam approach to understanding eigenfunction concentration. We characterize the features that cause an eigenfunction to saturate the standard supremum bounds in terms of the distribution of $L^{2}$ mass along geodesic tubes emanating from a point. We also show that the phenomena behind extreme supremum norm growth is identical to that underlying extreme growth of eigenfunctions when averaged along ...

35P20 ; 58J50 ; 53C22 ; 53C40 ; 53C21

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Aim of the lecture is to give an introduction to $K3$ surfaces, that are special algebraic surfaces with an extremely rich geometry. The most easy example of such a surface is the Fermat quartic in complex three-dimensional space.
The name $K3$ was given by André Weil in 1958 in honour of the three remarkable mathematicians: Kummer, Kähler and Kodaira and of the beautiful K2 mountain at Cachemire.
The topics of the lecture are the following:

* $K3$ surfaces in the Enriques-Kodaira classification.
* Examples; Kummer surfaces.
* Basic properties of $K3$ surfaces; Torelli theorem and surjectivity of the period map.
* The study of automorphisms on $K3$ surfaces: basic facts, examples.
* Symplectic automorphisms of $K3$ surfaces, classification, moduli spaces.
Aim of the lecture is to give an introduction to $K3$ surfaces, that are special algebraic surfaces with an extremely rich geometry. The most easy example of such a surface is the Fermat quartic in complex three-dimensional space.
The name $K3$ was given by André Weil in 1958 in honour of the three remarkable mathematicians: Kummer, Kähler and Kodaira and of the beautiful K2 mountain at Cachemire.
The topics of the lecture are the following:

* ...

14J10 ; 14J28 ; 14J50 ; 14C20 ; 14C22 ; 14J27 ; 14L30

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The Lüroth problem asks whether every unirational variety is rational. Over the complex numbers, it has a positive answer for curves and surfaces, but fails in higher dimensions. In this talk, I will consider the Lüroth problem for real algebraic varieties that are geometrically rational, and explain a counterexample not accounted for by the topology of the real locus or by unramified cohomology. This is joint work with Olivier Wittenberg.

14M20 ; 14E08

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Orders in finite-dimensional algebras over number fi give rise to interesting locally symmetric spaces and algebraic varieties. Hilbert modular varieties or arithmetically defined hyperbolic 3-manifolds, compact ones as well as noncompact ones, are familiar examples. In this talk we discuss various cases related to the general linear group $GL(2)$ over orders in division algebras defined over some number field. Geometry, arithmetic, and the theory of automorphic forms are interwoven in a most fruitful way in this work. Finally we indicate a construction of non-vanishing square-integrable cohomology classes for such arithmetically defined groups.
Orders in finite-dimensional algebras over number fi give rise to interesting locally symmetric spaces and algebraic varieties. Hilbert modular varieties or arithmetically defined hyperbolic 3-manifolds, compact ones as well as noncompact ones, are familiar examples. In this talk we discuss various cases related to the general linear group $GL(2)$ over orders in division algebras defined over some number field. Geometry, arithmetic, and the ...

11F75 ; 11F55

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Let $X$ be a compact Kähler manifold. The so-called Kodaira problem asks whether $X$ has arbitrarily small deformations to some projective varieties. While Kodaira proved that such deformations always exist for surfaces. Starting from dimension 4, there are examples constructed by Voisin which answer the Kodaira problem in the negative. In this talk, we will focus on threefolds, as well as compact Kähler manifolds of algebraic dimension $a(X) = dim(X) -1$. We will explain our positive solution to the Kodaira problem for these manifolds.
Let $X$ be a compact Kähler manifold. The so-called Kodaira problem asks whether $X$ has arbitrarily small deformations to some projective varieties. While Kodaira proved that such deformations always exist for surfaces. Starting from dimension 4, there are examples constructed by Voisin which answer the Kodaira problem in the negative. In this talk, we will focus on threefolds, as well as compact Kähler manifolds of algebraic dimension $a(X) = ...

32J17 ; 32J27 ; 32J25 ; 32G05 ; 14D06 ; 14E30

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​We consider photoacoustic tomography in the presence of approximation and modelling errors. The inverse problem, i.e. estimation of the initial pressure from photoacoustic time-series measured on the boundary of the target, is approached in the framework of Bayesian inverse problems. The posterior distribution is examined in situations in which the forward model contains errors or uncertainties for example due to numerical approximations or uncertainties in the acoustic parameters. Modelling of these errors and its impact on the posterior distribution are investigated.
This is joint work with Teemu Sahlstrm, Jenni Tick and Aki Pulkkinen.
​We consider photoacoustic tomography in the presence of approximation and modelling errors. The inverse problem, i.e. estimation of the initial pressure from photoacoustic time-series measured on the boundary of the target, is approached in the framework of Bayesian inverse problems. The posterior distribution is examined in situations in which the forward model contains errors or uncertainties for example due to numerical approximations or ...

35R30 ; 35Q60 ; 65R32 ; 65C20 ; 92C55

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The 1983 discovery of the fractional quantum Hall effect marks a milestone in condensed matter physics: systems of “ordinary particles at ordinary energies” displayed highly exotic effects, most notably fractional quantum numbers. It was later recognized that this was due to emergent quasi-particles carrying a fraction of the charge of an electron. It was also conjectured that these quasi-particles had fractional statistics, i.e. a behavior interpolating between that of bosons and fermions, the only two types of fundamental particles.
These lectures will be an introduction to the basic physics of the fractional quantum Hall effect, with an emphasis on the challenges to rigorous many-body quantum mechanics emerging thereof. Some progress has been made on some of these, but lots remains to be done, and open problems will be mentioned.

After the lectures a few references regarding the spectrum of the magnetic Schrödinger operator were suggested to me.
See the bibiography below.

Thank Alix Deleporte, Frédéric Faure, Stéphane Nonnenmacher and others for discussions relative to the magnetic Weyl law.
The 1983 discovery of the fractional quantum Hall effect marks a milestone in condensed matter physics: systems of “ordinary particles at ordinary energies” displayed highly exotic effects, most notably fractional quantum numbers. It was later recognized that this was due to emergent quasi-particles carrying a fraction of the charge of an electron. It was also conjectured that these quasi-particles had fractional statistics, i.e. a behavior ...

81V70 ; 81Sxx ; 81V35

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​I will discuss recent developments concerning the non-uniqueness of distributional solutions to the Navier-Stokes equation.

35Q30 ; 76D05 ; 35Q35

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A general introduction to the state of the art in counting of rational and integral points on varieties, using various analytic methods with the Brauer-Manin obstruction.

14G05 ; 14F22

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We will discuss several new ideas that can show the existence of jet differential operators on arbitrary projective varieties, and also on general hypersurfaces of $\mathbb{P}^n$ of sufficiently high degree. These results can be applied to improve degree bounds in several hyperbolicity problems and especially in the proof of the Kobayashi conjecture.

32Q45 ; 32L10 ; 53C55 ; 14J40

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Post-edited  Graph data management - part 1
Martens, Wim (Auteur de la Conférence) | CIRM (Editeur )

After giving a motivation of graph databases and an overview of the main data models, we will dive into foundational aspects of graph database query languages, with a strong focus on regular path queries (RPQs) and conjunctive regular path queries (CRPQs). We will consider the different semantics that graph database systems use for such queries (every path, simple path, trail), and we will look into the computational complexities of query evaluation and query containment.
After having gone through these foundations, we plan to do some excursions into connections between tree-structured and graph-structured data, adding data value comparisons, and aspects of real-life queries.
After giving a motivation of graph databases and an overview of the main data models, we will dive into foundational aspects of graph database query languages, with a strong focus on regular path queries (RPQs) and conjunctive regular path queries (CRPQs). We will consider the different semantics that graph database systems use for such queries (every path, simple path, trail), and we will look into the computational complexities of query ...

68P15 ; 68Q19

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Some convergence properties for the approximation of second order elliptic problems with a variety of boundary conditions (homogeneous Dirichlet, homogeneous or non-homogeneous Neumann or Fourier boundary conditions), using a given discretisation method, can be obtained when this method is plugged into the Gradient Discretisation Method (GDM) framework.
Instead of defining one GDM framework for each of these boundary conditions, we show that these properties can be stated using the same abstract tools for all the above boundary conditions. Then these tools enable the application of the GDM to a larger class of elliptic problems.
Some convergence properties for the approximation of second order elliptic problems with a variety of boundary conditions (homogeneous Dirichlet, homogeneous or non-homogeneous Neumann or Fourier boundary conditions), using a given discretisation method, can be obtained when this method is plugged into the Gradient Discretisation Method (GDM) framework.
Instead of defining one GDM framework for each of these boundary conditions, we show that ...

65J05 ; 65Nxx ; 47A58

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This course presents an overview of modern Bayesian strategies for solving imaging inverse problems. We will start by introducing the Bayesian statistical decision theory framework underpinning Bayesian analysis, and then explore efficient numerical methods for performing Bayesian computation in large-scale settings. We will pay special attention to high-dimensional imaging models that are log-concave w.r.t. the unknown image, related to so-called “convex imaging problems”. This will provide an opportunity to establish connections with the convex optimisation and machine learning approaches to imaging, and to discuss some of their relative strengths and drawbacks. Examples of topics covered in the course include: efficient stochastic simulation and optimisation numerical methods that tightly combine proximal convex optimisation with Markov chain Monte Carlo techniques; strategies for estimating unknown model parameters and performing model selection, methods for calculating Bayesian confidence intervals for images and performing uncertainty quantification analyses; and new theory regarding the role of convexity in maximum-a-posteriori and minimum-mean-square-error estimation. The theory, methods, and algorithms are illustrated with a range of mathematical imaging experiments.
This course presents an overview of modern Bayesian strategies for solving imaging inverse problems. We will start by introducing the Bayesian statistical decision theory framework underpinning Bayesian analysis, and then explore efficient numerical methods for performing Bayesian computation in large-scale settings. We will pay special attention to high-dimensional imaging models that are log-concave w.r.t. the unknown image, related to ...

49N45 ; 65C40 ; 65C60 ; 65J22 ; 68U10 ; 62C10 ; 62F15 ; 94A08

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Le but de ce cours sera de présenter quelques techniques liées aux processus de Schur, dans le cadre le plus simple de la mesure de Plancherel sur les partitions d'entiers.
La mesure de Plancherel est une mesure sur l'ensemble des partitions d'un entier n, où une partition donnée apparaît avec une probabilité proportionnelle au carré de son nombre de tableaux de Young standard. Cette mesure apparaît très naturellement en lien avec le fameux problème de Ulam-Hammersley, qui consiste à étudier la longueur d'une plus longue sous-suite croissante d'une permutation uniforme de {1,...,n}. Il est en fait fructueux de travailler avec une version "poissonisée" du problème, où la taille n est tirée selon une loi de Poisson, dont on fera tendre le paramètre vers l'infini afin d'étudier les asymptotiques.
Dans la première séance, nous verrons que la mesure de Plancherel poissonisée est en fait un processus déterminantal, dont le noyau de corrélation fait intervenir les fonctions de Bessel. Nous utiliserons pour cela le formalisme de l'espace de Fock fermionique. (Toutes les notions nécessaires seront introduites au fur et à mesure, de la manière la plus élémentaire possible.)
Dans la seconde séance, nous étudierons les différentes asymptotiques du noyau de corrélation, par une application élégante de la méthode du col due à Okounkov et Reshetikhin. Nous verrons en particulier apparaître un phénomène de forme-limite, le noyau sinus discret dans le cas des limites "bulk" et le noyau d'Airy dans la limite "edge". In fine, nous aboutirons à une preuve du théorème de Baik-Deift-Johansson (1998) énonçant que les fluctuations de la longueur d'une plus longue sous-suite croissante d'une permutation uniforme ont asymptotiquement la même distribution que la plus grande valeur propre d'une matrice hermitienne aléatoire.
Le but de ce cours sera de présenter quelques techniques liées aux processus de Schur, dans le cadre le plus simple de la mesure de Plancherel sur les partitions d'entiers.
La mesure de Plancherel est une mesure sur l'ensemble des partitions d'un entier n, où une partition donnée apparaît avec une probabilité proportionnelle au carré de son nombre de tableaux de Young standard. Cette mesure apparaît très naturellement en lien avec le fameux ...

05A17 ; 05E10 ; 60C05 ; 60G55

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Post-edited  Algebraicity of the metric tangent cones
Wang, Xiaowei (Auteur de la Conférence) | CIRM (Editeur )

We proved that any K-semistable log Fano cone admits a special degeneration to a uniquely determined K-polystable log Fano cone. This confirms a conjecture of Donaldson-Sun stating that the metric tangent cone of any close point appearing on a Gromov-Hausdorff limit of Kähler-Einstein Fano manifolds depends only on the algebraic structure of the singularity. This is a joint work with Chi Li and Chenyang Xu.

14J45 ; 32Q15 ; 32Q20 ; 53C55

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Multi angle  Zeros, moments and determinants
Snaith, Nina (Auteur de la Conférence) | CIRM (Editeur )

For 20 years we have known that average values of characteristic polynomials of random unitary matrices provide a good model for moments of the Riemann zeta function. Now we consider mixed moments of characteristic polynomials and their derivatives, calculations which are motivated by questions on the distribution of zeros of the derivative of the Riemann zeta function.

15B52 ; 11M26 ; 11M06

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Multi angle  When J. Ginibre met E. Schrödinger
Bothner, Thomas (Auteur de la Conférence) | CIRM (Editeur )

The real Ginibre ensemble consists of square real matrices whose entries are i.i.d. standard normal random variables. In sharp contrast to the complex and quaternion Ginibre ensemble, real eigenvalues in the real Ginibre ensemble attain positive likelihood. In turn, the spectral radius of a real Ginibe matrix follows a different limiting law for purely real eigenvalues than for non-real ones. Building on previous work by Rider, Sinclair and Poplavskyi, Tribe, Zaboronski, we will show that the limiting distribution of the largest real eigenvalue admits a closed form expression in terms of a distinguished solution to an inverse scattering problem for the Zakharov-Shabat system. This system is directly related to several of the most interesting nonlinear evolution equations in 1+1 dimensions which are solvable by the inverse scattering method, for instance the nonlinear Schr¨odinger equation. The results of this talk are based on the recent preprint arXiv:1808.02419, joint with Jinho Baik.
The real Ginibre ensemble consists of square real matrices whose entries are i.i.d. standard normal random variables. In sharp contrast to the complex and quaternion Ginibre ensemble, real eigenvalues in the real Ginibre ensemble attain positive likelihood. In turn, the spectral radius of a real Ginibe matrix follows a different limiting law for purely real eigenvalues than for non-real ones. Building on previous work by Rider, Sinclair and ...

60B20 ; 45M05 ; 60G70

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