In this talk I will discuss some of the ideas behind the difficult problem of computing the mean values of L-functions on the critical line. After a basic and brief discussion I will consider the same problem for function fields over a finite field, and in this case something `deeper’ can be said.

I will introduce the notion of fundamental groups and etale sheaves at a very elementary level. These are generalizations of the classical Galois theory and the usual fundamental groups. Also I will discuss certain problems on ramification of sheaves and degeneration of varieties.

Le théorème de Nekhoroshev garantit la stabilité, pendant un intervalle de temps exponentiellement long, des systèmes hamiltoniens qui sont proches des systèmes intégrables. C’est un résultat théorique, qui est hélas difficilement applicable à des systèmes hamiltoniens concrets. Le but de l’exposé est d’expliquer une variante de ce théorème de Nekhoroshev, plus flexible, que l’on espère pouvoir appliquer à des systèmes concrets tels que le problème à trois corps Soleil-Jupiter-Saturne.

Compactifications of M5-branes on non-trivial 3-manifolds lead to a N=2 supersymmetric theories in 3 dimensions. If the 3-manifold in question is a knot complement, various Chern-Simons amplitudes – or corresponding knot invariants – for this knot determine the properties of the resulting 3d, N=2 theory. This relation between N=2 theories and Chern-Simons theory is referred to as the 3d-3d correspondence. M-theory realization of this correspondence implies that N=2 theories obtained in this way possess one special flavor symmetry, which is related to certain deformation of Chern-Simons theory and homological knot invariants. In this talk I will discuss properties of these refined/homological invariants, and their role in the 3d-3d correspondence.

Dans cet exposé, j’expliquerai le comportement de la conjecture de Birch et Swinnerton-Dyer dans la Zp-extension cyclotomique : si p est un nombre premier ordinaire, il existe une fonction L p-adique classique, avec des invariants canoniques qui fournissent une description adéquate de ce comportement. Si p est un nombre premier supersingulier, on peut le décrire par une paire de fonctions L p-adiques (avec une paire d’invariants), auquel cas il y a des phénomènes mystérieux.

We define the characteristic cycle of a locally constant étale sheaf on a smooth variety in positive characteristic, ramified along the boundary, as a cycle in the cotangent bundle of the variety, at least on a neighborhood of the generic point of the divisor on the boundary.

We discuss a compatibility with pull-back and local acyclicity in non-characteristic situations. We also give a relation with the characteristic cohomology class and the Euler-Poincaré characteristic.

Geometric spaces are described by spectral triples (A, H, D) in non-commutative geometry. In this context, A is an involutive noncommutative algebra represented by bounded operators on a Hilbert space H, and D is an unbounded selfadjoint operator acting in H which plays the role of the Dirac operator, namely that it contains the metric information while interacting with the algebra in a bounded manner. The local geometric invariants such as the scalar curvature of (A, H, D) are extracted from the high frequency behavior of the spectrum of D and the action of A via special values and residues of the meromorphic extension of zeta functions ζa to the complex plane, which are defined for a in A by

ζa (s) = Trace (a ⎜D⎜-s),        ℜ(s) >> 0.

Following the seminal work of A. Connes and P. Tretkoff on the Gauss-Bonnet theorem for the canonical translation invariant conformal structure on the noncommutative two torus Tθ2, there have been significant developments in understanding the local differential geometry of these C*-algebras equipped with curved metrics. In this talk, I will review my joint works with M. Khalkhali, in which we extend this result to general translation invariant conformal structures on Tθ2 and compute the scalar curvature. Our final formula for the curvature matches precisely with the independent result of A. Connes and H. Moscovici. I will also present our recent work on noncommutative four tori, in which we compute the scalar curvature and show that the metrics with constant curvature are extrema of the analog of the Einstein-Hilbert action.

In this talk I will explain how to realize some powers of the Dedekind eta function as a trace formula via different quantum coordinate algebras associated to semi-simple Lie algebras. If time permits, I will mention several perspectives, including relations to the Lehmer’s conjecture on Ramanujan’s tau function, the quantum dilogarithms, etc…

La conjecture d'Ax-Lindemann hyperbolique est un énoncé de transcendance fonctionnelle concernant les morphismes d'uniformisation des variétés de Shimura par des espaces symétriques hermitiens. Ces derniers sont munis d'une structure semi-algébrique naturelle et la conjecture d'Ax-Lindemann hyperbolique décrit l'adhérence de Zariski des "flots algébriques" dans la variété de Shimura. Nous expliquerons la preuve récente de cette conjecture obtenue dans un travail en commun avec Bruno Klingler et Andrei Yafaev. Nous expliquerons aussi la place de cet énoncé dans la stratégie de Pila-Zannier pour une preuve inconditionnelle de la conjecture d'André-Oort. Nous montrerons en particulier comment on obtient la preuve de la conjecture d'André-Oort pour une puissance arbitraire du module des variétés abéliennes principalement polarisées de dimension 6.

By a function field K, we mean a field extension over a finite field with transcendence degree one. In the function field world, by the work of Deligne, Drinfeld, Jacquet-Langlands, Weil, and Zarhin, the « Drinfeld modular parametrization » always exists for every « non-isotrivial » elliptic curve E over K. Suppose E has split multiplicative reduction at a place ∞. Then there exists a unique « Drinfeld type » (with respect to ∞) automorphic cusp form fE such that its L-function coincides with the Hasse-Weil L-function of E over K. These forms can be viewed as analogue of classical weight 2 modular forms. In this talk, we will start with basic properties of Drinfeld type automorphic forms, and use them as tools to obtain explicit formulas for special values of the L-functions coming from non-isotrivial elliptic curves.