Cohomologie des espaces de formes automorphes
Let be a non-archimedean local field. This paper gives an explicit isomorphism between the dual of the special representation of and the space of harmonic cochains defined on the Bruhat-Tits building of , in the sense of E. de Shalit [11]. We deduce, applying the results of a paper of P. Schneider and U. Stuhler [9], that there exists a -equivariant isomorphism between the cohomology group of the Drinfeld symmetric space and the space of harmonic cochains.
Let be a prime and let be a -group of matrices in , for some integer . In this paper we show that, when , a certain subgroup of the cohomology group is trivial. We also show that this statement can be false when . Together with a result of Dvornicich and Zannier (see [2]), we obtain that any algebraic torus of dimension enjoys a local-global principle on divisibility by .
Let 𝓐₂(n) = Γ₂(n)∖𝔖₂ be the quotient of Siegel's space of degree 2 by the principal congruence subgroup of level n in Sp(4,ℤ). This is the moduli space of principally polarized abelian surfaces with a level n structure. Let 𝓐₂(n)* denote the Igusa compactification of this space, and ∂𝓐₂(n)* = 𝓐₂(n)* - 𝓐₂(n) its "boundary". This is a divisor with normal crossings. The main result of this paper is the determination of H(∂𝓐₂(n)*) as a module over the finite group Γ₂(1)/Γ₂(n). As an application...