Rationality of the moduli spaces of plane curves of sufficiently large degree
We prove that the moduli space of plane curves of degree d is rational for all sufficiently large d.
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arXiv subjects
Christian Böhning
Publications and source records attributed to Christian Böhning.
Derived categories of coherent sheaves on rational homogeneous manifolds
Starting point of the present work is a conjecture of F. Catanese which says that in the derived category of coherent sheaves on any rational homogeneous manifold G/P there should exist a complete strong exceptional poset and a bijection of the elements of the poset with the Schubert varieties in G/P such that the partial order on the poset is the order induced by the Bruhat-Chevalley order. The goal of this work is to provide further evidence for Catanese's conjecture, clarify some aspects of it and supply new techniques. In particular we prove a theorem on the derived categories of quadric bundles, and show how one can find "small" generating sets for D^b(X) on symplectic or orthogonal isotropic Grassmannians by fibrational techniques.- The last section discusses a different approach based on a theorem of M. Brion and cellular resolutions of monomial ideals.
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Canonical surfaces in P^4 and Gorenstein algebras in codimension 2
In this paper I investigate minimal surfaces of general type with p_g=5, q=0 for which the 1-canonical map is a birational morphism onto a surface in P^4 (so called canonical surfaces in P^4) via a structure theorem for the Hilbert resolutions of the canonical rings of the afore-mentioned surfaces, viewed as Gorenstein algebras of codimension 2 over the homogeneous coordinate ring of P^4. I discuss how the ring structure of such an algebra is encoded in its resolution. Among other things I show how this method can be applied to analyze the moduli space of canonical surfaces with p_g=5, q=0, K^2=11, thus recovering a result previously obtained by D. Rossberg with different techniques.
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L. Szpiro's conjecture on Gorenstein algebras in codimension 2
A Gorenstein A-algebra R of codimension 2 is a perfect finite A-algebra such that R=Ext^2(R,A) holds as R-modules, A being a Cohen-Macaulay local ring with dim(A)-dim_A(R)=2. I prove a structure theorem for these algebras improving on an old theorem of M. Grassi. Special attention is paid to the question how the ring structure of R is encoded in its Hilbert resolution. It is shown that R is automatically a ring once one imposes a weak depth condition on a determinantal ideal derived from a presentation matrix of R over A. The interplay of Gorenstein algebras and Koszul modules as introduced by M. Grassi is clarified. Questions of applicability to canonical surfaces in P^4 have served as a guideline in these investigations.
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