Cartan Projections of some Nonreductive Subgroups

par Prof. Yosuke Morita (Université de Kyoto & IHES)

mardi 28 janv. 2020, 11:30 → 12:30 Europe/Paris

Amphithéâtre Léon Motchane (IHES)

Let G be a real reductive Lie group and H a closed subgroup of G. According to the Benoist-Kobayashi criterion, the properness of an action on G/H is controlled by the Cartan projection of H. In this talk, we give some examples of closed subgroups that are not reductive in G but whose Cartan projection is computable (one example is an abelian horospherical subgroup of G). Applying these nonreductive subgroups, we show that some homogeneous spaces of reductive type do not have compact Clifford-Klein forms.