On SL(2)-actions without 3-dimensional orbits
On some geometric aspects of Bruhat orderings. I. A finer decomposition of Bruhat cells.
On some reductive group actions on affine space II.
On some symplectic quotients of Schubert varieties.
On spherical nilpotent orbits and beyond
We continue investigations that are concerned with the complexity of nilpotent orbits in semisimple Lie algebras. We give a characterization of the spherical nilpotent orbits in terms of minimal Levi subalgebras intersecting them. This provides a kind of canonical form for such orbits. A description minimal non-spherical orbits in all simple Lie algebras is obtained. The theory developed for the adjoint representation is then extended to Vinberg’s -groups. This yields a description of spherical...
On spinor varieties and their secants.
On symmetric semialgebraic sets and orbit spaces
For a symmetric (= invariant under the action of a compact Lie group G) semialgebraic basic set C, described by s polynomial inequalities, we show, that C can also be written by s + 1 G-invariant polynomials. We also describe orbit spaces for the action of G by a number of inequalities only depending on the structure of G.
On the calculation of some differential galois groups.
On the Classification of Commutative Formal Group Laws over p-Hilbert Domains and a Finiteness Theorem for Higher Hasse-Witt Matrices.
On the complicatedness of the pair (g,K).
On the congruence subgroup problem
On the Connected Part of the Covariant Tate p-divisible Group and the ?-function of the Family of Hyperelliptic Curves y2 = 1 + ? xN Modulo Various Primes.
On the Converse of Abel's Theorem in Characteristic p.
On the Covariant Dieudonné-Module of an Abelian Variety of Dimension Two over W(k).
On the de Rham isomorphism for Drinfeld modules.
On the Euler number of an orbifold.
On the geometry of conjugacy classes in classical groupes.
On the geometry of moduli of curves and line bundles
Here we focus on the geometry of , the compactification of the universal Picard variety constructed by L. Caporaso. In particular, we show that the moduli space of spin curves constructed by M. Cornalba naturally injects into and we give generators and relations of the rational Picard group of , extending previous work by A. Kouvidakis.
On the height of Calabi-Yau varieties in positive characteristic.
On the linearization of actions of linearly reductive groups.