Pieri Type formula for isotropic Grassmannians; the operator approach.
Pieri's formula for flag manifolds and Schubert polynomials
We establish the formula for multiplication by the class of a special Schubert variety in the integral cohomology ring of the flag manifold. This formula also describes the multiplication of a Schubert polynomial by either an elementary or a complete symmetric polynomial. Thus, we generalize the classical Pieri’s formula for Schur polynomials (associated to Grassmann varieties) to Schubert polynomials (associated to flag manifolds). Our primary technique is an explicit geometric description of certain...
Pieri-type formulas for maximal isotropic Grassmannians via triple intersections
We give an elementary proof of the Pieri-type formula in the cohomology ring of a Grassmannian of maximal isotropic subspaces of an orthogonal or symplectic vector space. This proof proceeds by explicitly computing a triple intersection of Schubert varieties. The multiplicities (which are powers of 2) in the Pieri-type formula are seen to arise from the intersection of a collection of quadrics with a linear space.
Pieri-type intersection formulas and primary obstructions for decomposing 2-forms
We study the homological intersection behaviour for the Chern cells of the universal bundle of G(d,Qₙ), the space of [d]-planes in the smooth quadric Qₙ in over the field of complex numbers. For this purpose we define some auxiliary cells in terms of which the intersection properties of the Chern cells can be described. This is then applied to obtain some new necessary conditions for the global decomposability of a 2-form of constant rank.
Pinceaux de droites et automorphismes des surfaces affines.
Plongements d'espaces homogènes.
Plongements d'espaces symétriques algébriques : une classification
Pluripolar sets in Grassmann manifolds
Points entiers dans les polytopes convexes
Points non factoriels des variétés de modules de faisceaux semi-stables sur une surface rationnelle.
Points rationnels et groupes fondamentaux : applications de la cohomologie -adique
Je présenterai des résultats de T. Ekedahl et H. Esnault sur les variétés projectives lisses sur un corps de caractéristique strictement positive, disons , dont deux points peuvent être liés par une chaîne de courbes rationnelles, par exemple faiblement unirationnelles, ou de Fano. Notamment : 1) sur un corps fini, de telles variétés ont un point rationnel, résultat qui généralise le théorème de Chevalley-Warning ; 2) sur un corps algébriquement clos, de telles variétés ont un groupe fondamental...
Poisson geometry of directed networks in an annulus
As a generalization of Postnikov’s construction [P], we define a map from the space of edge weights of a directed network in an annulus into a space of loops in the Grassmannian. We then show that universal Poisson brackets introduced for the space of edge weights in [GSV3] induce a family of Poisson structures on rational matrix-valued functions and on the space of loops in the Grassmannian. In the former case, this family includes, for a particular kind of networks, the Poisson bracket associated...
Polar classes of singular varieties
Polyèdre de Newton et distribution f... +. II.
Polygons with hidden vertices.
Polynomials homologically supported on degeneracy loci
Polytopal linear algebra.
Polytopes secondaires et discriminants
Positive polynomials and hyperdeterminants
Let F be a homogeneous real polynomial of even degree in any number of variables. We consider the problem of giving explicit conditions on the coefficients so that F is positive definite or positive semi-definite. In this note we produce a necessary condition for positivity, and a sufficient condition for non-negativity, in terms of positivity or semi-positivity of a one-variable characteristic polynomial of F. Also, we revisit the known sufficient condition in terms of Hankel matrices.
Positivity and Kleiman transversality in equivariant -theory of homogeneous spaces
We prove the conjectures of Graham–Kumar [GrKu08] and Griffeth–Ram [GrRa04] concerning the alternation of signs in the structure constants for torus-equivariant -theory of generalized flag varieties . These results are immediate consequences of an equivariant homological Kleiman transversality principle for the Borel mixing spaces of homogeneous spaces, and their subvarieties, under a natural group action with finitely many orbits. The computation of the coefficients in the expansion of the equivariant...