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Smoothness of the invariant Hilbert scheme of affine spherical varieties for the existence of wonderful varieties


Let G be a reductive linear algebraic group over the complex numbers. A G-variety, an algebraic variety with an algebraic action of the group G, is said to be spherical if it is normal and has an open orbit for a maximal connected solvable subgroup of G. We aim to complete the classification of spherical varieties by proving Luna's conjecture on a special class of spherical varieties, called wonderful. To a wonderful variety one can naturally associate an invariant combinatorial object in terms of roots and weights, called spherical system. Luna's conjecture states that there exists a one-to-one correspondence between isomorphism classes of wonderful varieties and spherical systems. Given a spherical system, here we want to provide the corresponding wonderful variety by studying the geometric properties of a certain algebraic scheme, called invariant Hilbert scheme, recently introduced by Alexeev and Brion. The given reductive group G acts linearly on the ring of regular functions of any affine spherical G-variety, the corresponding linear representation is multiplicity-free. The invariant Hilbert scheme of Alexeev and Brion parameterises the affine spherical G-varieties with a fixed multiplicity-free representation in their ring of regular functions. It is endowed with an action of a maximal torus of the group G. Given a spherical system, the strategy is to define a suitable multiplicity-free representation and study the corresponding invariant Hilbert scheme. Via deformation theory arguments we want to prove that under certain conditions the considered invariant Hilbert scheme has an open orbit for the toric action. By a standard procedure, called spherical closure, one can associate to any spherical variety a wonderful variety. Here we want to prove that to an affine spherical variety corresponding to a generic point in the invariant Hilbert scheme it is associated a wonderful variety with the given spherical system.

Call for proposal

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Funding Scheme

MC-IEF - Intra-European Fellowships (IEF)


Avenue Centrale, Domaine Universitaire 621
38041 Grenoble
Activity type
Higher or Secondary Education Establishments
EU contribution
€ 82 568,49
Administrative Contact
Michel Brion (Prof.)