sentences:  Châu first came to prominence by proving, in joint work with Gérard Laumon, the fundamental lemma for unitary groups.Their general strategy was to understand the local orbital integrals appearing in the fundamental lemma in terms of affine Springer fibers arising in the Hitchin fibration.This allowed them to employ the tools of geometric representation theory, namely the theory of perverse sheaves, to study what was initially a combinatorial problem of a number-theoretic nature.