Holomorphic Maps of Generalized Iwasawa Manifolds.
We prove that the exceptional complex Lie group has a transitive action on the hyperplane section of the complex Cayley plane . Although the result itself is not new, our proof is elementary and constructive. We use an explicit realization of the vector and spin actions of . Moreover, we identify the stabilizer of the -action as a parabolic subgroup (with Levi factor ) of the complex Lie group . In the real case we obtain an analogous realization of .
These notes present some fundamental results and examples in the theory of algebraic group actions, with special attention to the topics of geometric invariant theory and of spherical varieties. Their goal is to provide a self-contained introduction to more advanced lectures.
Let be a split semisimple linear algebraic group over a field and let be a split maximal torus of . Let be an oriented cohomology (algebraic cobordism, connective -theory, Chow groups, Grothendieck’s , etc.) with formal group law . We construct a ring from and the characters of , that we call a formal group ring, and we define a characteristic ring morphism from this formal group ring to where is the variety of Borel subgroups of . Our main result says that when the torsion index...
Let be a semisimple linear algebraic group of inner type over a field , and let be a projective homogeneous -variety such that splits over the function field of . We introduce the -invariant of which characterizes the motivic behavior of , and generalizes the -invariant defined by A. Vishik in the context of quadratic forms. We use this -invariant to provide motivic decompositions of all generically split projective homogeneous -varieties, e.g. Severi-Brauer varieties, Pfister quadrics,...
These notes contain an introduction to the theory of spherical and wonderful varieties. We describe the Luna-Vust theory of embeddings of spherical homogeneous spaces, and explain how wonderful varieties fit in the theory.