Symplectic Topology and Extemal Rays.
Systolic invariants of groups and -complexes via Grushko decomposition
We prove a finiteness result for the systolic area of groups. Namely, we show that there are only finitely many possible unfree factors of fundamental groups of -complexes whose systolic area is uniformly bounded. We also show that the number of freely indecomposable such groups grows at least exponentially with the bound on the systolic area. Furthermore, we prove a uniform systolic inequality for all -complexes with unfree fundamental group that improves the previously known bounds in this dimension....
The conjugacy problem for relatively hyperbolic groups.
The diameter function on the space of space form
The Existence of Polarized F-structure on Volume Collapsed 4-manifolds.
The filling radius of homogeneous manifolds
The isometry groups of Riemannian orbifolds.
The Morse landscape of a riemannian disk
We study upper bounds on the length functional along contractions of loops in Riemannian disks of bounded diameter and circumference. By constructing metrics adapted to imbedded trees of increasing complexity, we reduce the nonexistence of such upper bounds to the study of a topological invariant of imbedded finite trees. This invariant is related to the complexity of the binary representation of integers. It is also related to lower bounds on the number of points in level sets of a real-valued...
The proportionality constant for the simplicial volume of locally symmetric spaces
We follow ideas going back to Gromov's seminal article [Publ. Math. IHES 56 (1982)] to show that the proportionality constant relating the simplicial volume and the volume of a closed, oriented, locally symmetric space M = Γ∖G/K of noncompact type is equal to the Gromov norm of the volume form in the continuous cohomology of G. The proportionality constant thus becomes easier to compute. Furthermore, this method also gives a simple proof of the proportionality principle for arbitrary manifolds.
The Trapping Property of Totally Geodesic Hyperplanes in Hadamard Spaces.
Théorème de la sphère
Trees of manifolds and boundaries of systolic groups
We prove that the Pontryagin sphere and the Pontryagin nonorientable surface occur as the Gromov boundary of a 7-systolic group acting geometrically on a 7-systolic normal pseudomanifold of dimension 3.
Un principe de concentration-compacité pour les suites de surfaces Riemanniennes
Uniformly Convex Metric Spaces
In this paper the theory of uniformly convex metric spaces is developed. These spaces exhibit a generalized convexity of the metric from a fixed point. Using a (nearly) uniform convexity property a simple proof of reflexivity is presented and a weak topology of such spaces is analyzed. This topology, called coconvex topology, agrees with the usually weak topology in Banach spaces. An example of a CAT(0)-space with weak topology which is not Hausdorff is given. In the end existence and uniqueness...
Vanishing of the first reduced cohomology with values in an -representation
We prove that the first reduced cohomology with values in a mixing -representation, , vanishes for a class of amenable groups including connected amenable Lie groups. In particular this solves for this class of amenable groups a conjecture of Gromov saying that every finitely generated amenable group has no first reduced -cohomology. As a byproduct, we prove a conjecture by Pansu. Namely, the first reduced -cohomology on homogeneous, closed at infinity, Riemannian manifolds vanishes. We also...
Variétés riemanniennes isométriques à l'infini.
Dans cet article, nous nous intéresserons à certaines propriétés des variétés riemanniennes non compactes qui ne dépendant que de leur géométrie à l'infini; pour cela, nous utiliserons un procédé de discrétisation qui associe un graph (pondéré) à une variété.
Volume et entropie minimale des espaces localement symétriques.
Volume of spheres in doubling metric measured spaces and in groups of polynomial growth
Let be a compactly generated locally compact group and let be a compact generating set. We prove that if has polynomial growth, then is a Følner sequence and we give a polynomial estimate of the rate of decay of Our proof uses only two ingredients: the doubling property and a weak geodesic property that we call Property (M). As a matter of fact, the result remains true in a wide class of doubling metric measured spaces including manifolds and graphs. As an application, we obtain a -pointwise...
Volume simplicial des espaces hermitiens symétriques
Volumes, courbure de Ricci et convergence des variétés