The maximal unipotent finite quotient, unusual torsion in Fano threefolds, and exceptional Enriques surfaces

Autor: Andrea Fanelli, Stefan Schröer
Jazyk: English<br />French
Rok vydání: 2020
Předmět:
Zdroj: Épijournal de Géométrie Algébrique, Vol Volume 4 (2020)
Druh dokumentu: article
ISSN: 2491-6765
DOI: 10.46298/epiga.2020.volume4.6151
Popis: We introduce and study the maximal unipotent finite quotient for algebraic group schemes in positive characteristics. Applied to Picard schemes, this quotient encodes unusual torsion. We construct integral Fano threefolds where such unusual torsion actually appears. The existence of such threefolds is surprising, because the torsion vanishes for del Pezzo surfaces. Our construction relies on the theory of exceptional Enriques surfaces, as developed by Ekedahl and Shepherd-Barron.
Databáze: Directory of Open Access Journals