Heights of varieties in multiprojective spaces and arithmetic Nullstellensätze

Nous présentons des bornes pour les degrés et hauteurs des polynômes apparaissant dans certains problèmes de géométrie algébrique effective, dont l'implicitation d'applications rationnelles et le Nullstellensatz effectif sur une variété. Notre traitement est basé sur la théorie de l'intersection arithmétique dans un produit d'espaces projectifs. Il étend au cadre arithmétique des constructions et résultats dus à Jelonek. Un rôle central est joué par la notion de hauteur canonique mixte d'une variété multiprojective. Nous étudions cette notion à l'aide de la théorie des résultants et nous montrons quelques-unes de ses propriétés de base, y compris son comportement par rapport aux intersections, projections et produits. Nous obtenons aussi des résultats analogues dans le cas d'un corps de fonctions, dont un Nullstellensatz paramétrique.We present bounds for the degree and the height of the polynomials arising in some problems in effective algebraic geometry including the implicitization of rational maps and the effective Nullstellensatz over a variety. Our treatment is based on arithmetic intersection theory in products of projective spaces and extends to the arithmetic setting constructions and results due to Jelonek. A key role is played by the notion of canonical mixed height of a multiprojective variety. We study this notion from the point of view of resultant theory and establish some of its basic properties, including its behavior with respect to intersections, projections and products. We obtain analogous results for the function field case, including a parametric Nullstellensatz.Fil: D'andrea, Carlos. Universidad de Barcelona; EspañaFil: Krick, Teresa Elena Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Investigaciones Matemáticas "Luis A. Santaló"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Matemática; ArgentinaFil: Sombra, Martín. Universidad de Barcelona; Españ

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Heights of varieties in multiprojective spaces and arithmetic Nullstellensätze

We present bounds for the degree and the height of the polynomials arising in some problems in effective algebraic geometry including the implicitization of rational maps and the effective Nullstellensatz over a variety. Our treatment is based on arithmetic intersection theory in products of projective spaces and extends to the arithmetic setting constructions and results due to Jelonek. A key role is played by the notion of canonical mixed heights of multiprojective varieties. We study this notion from the point of view of resultant theory and establish some of its basic properties, including its behavior with respect to intersections, projections and products. We obtain analogous results for the function field case, including a parametric Nullstellensatz