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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...
We discuss the problem of stable conjugacy of finite subgroups of Cremona groups. We compute the stable birational invariant H 1(G, Pic(X)) for cyclic groups of prime order.
Let be a prime integer and a field of characteristic . Let be thenorm varietyof a symbol in the Galois cohomology group (for some ), constructed in the proof of the Bloch-Kato conjecture. The main result of the paper affirms that the function field has the following property: for any equidimensional variety , the change of field homomorphism of Chow groups with coefficients in integers localized at is surjective in codimensions . One of the main ingredients of the proof is a computation...
The moduli space M of surfaces of general type with pg = q = 1, K2 = g = 3 (where g is the genus of the Albanese fibration) was constructed by Catanese and Ciliberto in [14]. In this paper we characterize the subvariety M2 ⊂ M corresponding to surfaces containing a genus 2 pencil, and moreover we show that there exists a non-empty, dense subset M0 ⊂ M which parametrizes isomorphism classes of surfaces with birational bicanonical map.
This paper classifies surfaces of general type with having an involution such that has non-negative Kodaira dimension and that the bicanonical map of factors through the double cover induced by It is shown that is regular and either: a) the Albanese fibration of is of genus 2 or b) has no genus 2 fibration and is birational to a surface. For case a) a list of possibilities and examples are given. An example for case b) with is also constructed.
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