On the maximum number of complexes of a given degree containing subvarieties of Grassmannians

Abstract

Let $\G(k,r)$ be the Grassmannian of $k$--subspaces in $\Proj^r$ embedded in $\Proj^{N(k,r)}$, with $N(k,r)={{r+1}\choose {k+1}}-1$, via the Pl\"ucker embedding. In this paper, extending some classical results by Gallarati (see \cite {Gal1,Gal2}), we give a sharp upper bound for the number of independent sections of $H^0(\G(k,r), \O_{\G(k,r)}(m))$ vanishing on a subvariety $X$ of $\G(k,r)$ such that the union of the $k$--subspaces corresponding to the points of $X$ spans $\Proj^r$.