On Orbit Closures of Spherical Subgroups in Flag Varieties
نویسنده
چکیده
Let F be the ag variety of a complex semi-simple group G, let H be an algebraic subgroup of G acting on F with nitely many orbits, and let V be an H-orbit closure in F. Expanding the cohomology class of V in the basis of Schubert classes deenes a union V 0 of Schubert varieties in F with positive multiplicities. If G is simply-laced, we show that these multiplicites are equal to the same power of 2. For arbitrary G, we show that V 0 is connected in codimension 1. If moreover all multiplicities are 1, we show that the singularities of V are rational and we construct a at degeneration of V to V 0 in F. Thus, for any eeective line bundle
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تاریخ انتشار 2007