L-modules and the Conjecture of Rapoport and Goresky-MacPherson

Sur le lemme fondamental pour les groupes unitaires

Assuming the purity conjecture for the affine Springer fibers which has been formulated by Goresky, Kottwitz and MacPherson, we prove a geometric analog of the fundamental lemma for unitary groups. Our approach is similar to the one of Goresky, Kottwitz and MacPherson. Our main new ingredient is the link between affine Springer fibers and compactified Jacobians which is described in math.AG/0204109.

L-模与微支撑

L-modules and micro-support

本文定义L-模的微支撑，证明消没定理，计算中间权重与中间异度L-模的微支撑，并应用解决Rapoport及Goresky-MacPherson猜想，推广加权上同调结果。

$\mathbf{GL}_{n}$ 的各向异性仿射 Springer 纤维的纯度

Purity of the anisotropic affine Springer fibers for $\mathbf{GL}_{n}$

对于 $\mathrm{GL}_{n}$ 群和各向异性元素，证明了 Goresky-Kottwitz-MacPherson 的纯度猜想，即仿射 Springer 纤维在 Grothendieck-Deligne 意义上是上同调纯的。

On the Cohomology of Locally Symmetric Spaces and of their Compactifications

This expository article is an expanded version of talks given at the "Current Developments in Mathematics, 2002" conference. It gives an introduction to the (generalized) conjecture of Rapoport and Goresky-MacPherson which identifies the intersection cohomology of a real equal-rank Satake compactification of a locally symmetric space with that of the reductive Borel-Serre compactification. We motivate the conjecture with examples and then give an introduction to the various topics that are involved: intersection cohomology, the derived category, and compactifications of a locally symmetric spa…

Complexes d'intersection des compactifications de Baily-Borel : Le cas des variétés de Siegel

In this work, we calculate the trace of a Hecke correspondance composed with a power of the Frobenius endomorphism on the fibre of the intersection complexes of the Baily-Borel compactification of a Siegel modular variety. Our main tool is Pink's theorem about the restriction to the strata of the Baily-Borel compactification of the direct image of a local system on the Shimura variety. To use this theorem, we give a new construction of the intermediate extension of a pure perverse sheaf as a weight truncation of the full direct image. More generally, we are able to define analogs in positive c…

The rational cohomology ring of the moduli space of abelian 3-folds

The rational cohomology ring of A_3, the moduli space of abelian 3-folds is computed. This is isomorphic to the the rational cohomology ring of the group Sp_3(Z) of 6x6 integral symplectic matrices. The main ingredients in the computation are (1) Looijenga's computation of the rational cohomology ring of M_3, the moduli space of smooth projective curves of genus 3, and (2) the stratified Morse theory of Goresky and MacPherson, which we use to compute the homology of the jacobian locus (in the rank 3 Siegel upper half plane), or equivalently of the extended Torelli group in genus 3. In the revi…