arXiv subjects
Publications and source records attributed to P. Deligne.
Consider a Chevalley group over a finite field $F_q$ such that the longest element of the Weyl group is central. We construct an involution $ξ\mapstoξ^!$ of the set of unipotent representations of this group such that the degree polynomial of a unipotent representation $ξ$ is obtained up to sign from the degree polynomial of $ξ^!$ by changing $q$ to $-q$.
Consider a Chevalley group over a finite field F_q such that the longest element in the Weyl group is central. In this paper we study the effect of changing q to -q in the polynomials which give the character values of unipotent representations of our group at semisimple elements.
Let $G$ be a reductive group over a field $k$ which is algebraically closed of characteristic $p \neq 0$. We prove a structure theorem for a class of subgroup schemes of $G$, for $p$ bounded below by the Coxeter number of $G$. As applications, we derive semi-simplicity results, generalizing earlier results of Serre proven in 1998, and also obtain an analogue of Luna's étale slice theorem for suitable bounds on $p$.
We give a new proof, inspired by an argument of Atiyah, Bott and Patodi, of the first fundamental theorem of invariant theory for the orthosymplectic super group. We treat in a similar way the case of the periplectic super group. Lastly, the same method is used to explain the fact that Sergeev's super Pfaffian, an invariant for the special orthosymplectic super group, is polynomial.
We define the category of mixed Tate motives over the ring of S-integers of a number field. We define the motivic fundamental group (made unipotent) of a unirational variety over a number field. We apply this to the study of the motivic fundamental group of the projective line punctured at zero, infinity and all N-th roots of unity.