ALGB Seminar: Jean-Pierre Tignol (Université Catholique de Louvain)
Title: Outer automorphisms of algebraic groups
Abstract: For an absolutely simple linear algebraic group that is simply connected or adjoint, the action of the automorphism group of the Dynkin diagram on the Tits class provides an obstruction to the existence of outer automorphisms. This talk will report on a joint work with Anne Quéguiner-Mathieu, in which we give examples where outer automorphisms do not exist, even though the Tits class obstruction vanishes. This settles in the negative a conjecture of Garibaldi-Petersson.