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EnglishWe study congruences of lines Xω defined by a sufficiently general choice of an alternating 3-form ω in n+1 dimensions, as Fano manifolds of index 3 and dimension n−1. These congruences include the G2-variety for n=6 and the variety of reductions of projected ℙ2×ℙ2 for n=7. We compute the degree of Xω as the n-th Fine number and study the Hilbert scheme of these congruences proving that the choice of ω bijectively corresponds to Xω except when n=5. The fundamental locus of the congruence is also studied together with its singular locus: these varieties include the Coble cubic for n=8 and the Peskine variety for n=9. The residual congruence Y of Xω with respect to a general linear congruence containing Xω is analysed in terms of the quadrics containing the linear span of Xω. We prove that Y is Cohen-Macaulay but non-Gorenstein in codimension 4. We also examine the fundamental locus G of Y of which we determine the singularities and the irreducible components.
| Titolo: | Fano congruences of index 3 and alternating 3-forms |
| Autori: | |
| Data di pubblicazione: | 2017 |
| Stato di pubblicazione: | Pubblicato |
| Rivista: | |
| Abstract: | We study congruences of lines Xω defined by a sufficiently general choice of an alternating 3-form ω in n+1 dimensions, as Fano manifolds of index 3 and dimension n−1. These congruences include the G2-variety for n=6 and the variety of reductions of projected ℙ2×ℙ2 for n=7. We compute the degree of Xω as the n-th Fine number and study the Hilbert scheme of these congruences proving that the choice of ω bijectively corresponds to Xω except when n=5. The fundamental locus of the congruence is also studied together with its singular locus: these varieties include the Coble cubic for n=8 and the Peskine variety for n=9. The residual congruence Y of Xω with respect to a general linear congruence containing Xω is analysed in terms of the quadrics containing the linear span of Xω. We prove that Y is Cohen-Macaulay but non-Gorenstein in codimension 4. We also examine the fundamental locus G of Y of which we determine the singularities and the irreducible components. |
| Handle: | http://hdl.handle.net/11368/2914428 |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.5802/aif.3131 |
| URL: | http://aif.cedram.org/cedram-bin/article/AIF_2017__67_5_2099_0.pdf |
| Appare nelle tipologie: | 1.1 Articolo in Rivista |
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| File | Descrizione | Tipologia | Licenza | |
|---|---|---|---|---|
| AIF_2017__67_5_2099_0.pdf | Articolo principale | Documento in Versione Editoriale |  | Open Access Visualizza/Apri |
http://hdl.handle.net/11368/2914428
