Rational projectively Cohen-Macaulay surfaces of maximum degree.
In this paper we determine the greatest degree of a rational projectively Cohen-Macaulay (p.C.M.) surface V in PN and we study the surfaces which attain such maximum degree.
In this paper we determine the greatest degree of a rational projectively Cohen-Macaulay (p.C.M.) surface V in PN and we study the surfaces which attain such maximum degree.
We study the Zariski closures of orbits of representations of quivers of type , ou . With the help of Lusztig’s canonical base, we characterize the rationally smooth orbit closures and prove in particular that orbit closures are smooth if and only if they are rationally smooth.
Let p be a prime greater than 3. Consider the modular curve X₀(3p) over ℚ and its Jacobian variety J₀(3p) over ℚ. Let (3p) and (3p) be the group of rational torsion points on J₀(3p) and the cuspidal group of J₀(3p), respectively. We prove that the 3-primary subgroups of (3p) and (3p) coincide unless p ≡ 1 (mod 9) and .
Dans l’exposé Bourbaki 409, Katz conjecture la méromorphie -adique de la fonction attachée à une variété lisse sur un corps fini () et à un -cristal sur . Si est propre et lisse sur nous prouvons que est rationnelle et fournie par l’expression habituelle utilisant l’action du Frobenius sur la cohomologie cristalline à coefficients dans ; ce résultat n’était connu, via les “conjectures de Weil”, que pour des -cristaux unités particuliers: ceux provenant d’une représentation de...
Let be a field of characteristic zero and G be a finite group of automorphisms of projective plane over . Castelnuovo’s criterion implies that the quotient of projective plane by G is rational if the field is algebraically closed. In this paper we prove that is rational for an arbitrary field of characteristic zero.