Konstantenreduktion von Ringen und Moduln.
Maximal compatible splitting and diagonals of Kempf varieties
Lakshmibai, Mehta and Parameswaran (LMP) introduced the notion of maximal multiplicity vanishing in Frobenius splitting. In this paper we define the algebraic analogue of this concept and construct a Frobenius splitting vanishing with maximal multiplicity on the diagonal of the full flag variety. Our splitting induces a diagonal Frobenius splitting of maximal multiplicity for a special class of smooth Schubert varieties first considered by Kempf. Consequences are Frobenius splitting of tangent bundles,...
On the divisibility properties of families of filtered F-crystals.
On the field of definition of superspecial polarized abelian varieties and type numbers
On the number of compatibly Frobenius split subvarieties, prime -ideals, and log canonical centers
Let be a projective Frobenius split variety with a fixed Frobenius splitting . In this paper we give a sharp uniform bound on the number of subvarieties of which are compatibly Frobenius split with . Similarly, we give a bound on the number of prime -ideals of an -finite -pure local ring. Finally, we also give a bound on the number of log canonical centers of a log canonical pair. This final variant extends a special case of a result of Helmke.
On the uniform behaviour of the Frobenius closures of ideals
Let be a proper ideal of a commutative Noetherian ring R of prime characteristic p and let Q() be the smallest positive integer m such that , where is the Frobenius closure of . This paper is concerned with the question whether the set is bounded. We give an affirmative answer in the case that the ideal is generated by an u.s.d-sequence c₁,..., cₙ for R such that (i) the map induced by multiplication by c₁...cₙ is an R-monomorphism; (ii) for all , c₁/1,..., cₙ/1 is a -filter regular sequence...
Regularity and intersections of bracket powers
Among reduced Noetherian prime characteristic commutative rings, we prove that a regular ring is precisely that where the finite intersection of ideals commutes with taking bracket powers. However, reducedness is essential for this equivalence. Connections are made with Ohm-Rush content theory, intersection-flatness of the Frobenius map, and various flatness criteria.
Some surprising Hilbert-Kunz functions.
Sur la compatibilité à Frobenius de l’isomorphisme de dualité relative
The injectivity of Frobenius acting on cohomology and local cohomology modules.
The Picard group and subintegrality in positive characteristic
Théorie de Fontaine en égales caractéristiques
Les chtoucas locaux sont des analogues en égales caractéristiques des groupes -divisibles — par exemple on leur associe un module de Tate, qui est un module libre sur l’anneau d’entiers d’un corps local de caractéristique positive. Nous associons à un chtouca local une structure de Hodge (ou, plus précisément, une structure de Hodge-Pink), ce qui induit un morphisme de périodes analogue à celui construit par Rapoport et Zink. Pour les structures de Hodge-Pink définies sur une extension finie...
Tight closure and the Kodaira Vanishing Theorem.
Tight closure of an ideal generated by an R-sequence.
Tight closure of parameter ideals.
When does the -signature exist?
We show that the -signature of an -finite local ring of characteristic exists when is either the localization of an -graded ring at its irrelevant ideal or -Gorenstein on its punctured spectrum. This extends results by Huneke, Leuschke, Yao and Singh and proves the existence of the -signature in the cases where weak -regularity is known to be equivalent to strong -regularity.