%0 Journal Article
%T Spherical Hall algebras of curves and Harder-Narasimhan stratas
%A Olivier Schiffmann
%J Mathematics
%D 2010
%I arXiv
%X Let X be any smooth projective curve defined over a finite field. We show that the characteristic functions of any Harder-Narasimhan strata S_a of Bun_{GL_n}X belongs to the spherical Hall algebra H_X^{sph} of X. We give a geometric analog of the above result: the intersection cohomology sheaf IC(S_a) belongs to the category of simple Eisenstein sheaves over Bun_{GL_n}X.
%U http://arxiv.org/abs/1002.0987v1