Uniform non-homogeneous bundles on quadrics

Abstract

Let $X$ be an $n$-dimensional generalized Grassmannian not isomorphic to ${\mathbb{P}}^n$. We prove that $k(X)\le n-1$, where $k(X)$ denotes the maximal integer such that every uniform bundle on $X$ of rank at most $k(X)$ is homogeneous. In particular, for smooth quadrics ${\mathbb{Q}}^n$, we have $k({\mathbb{Q}}^n)=n-1$ for odd $n$, and $n-2\le k({\mathbb{Q}}^n)\le n-1$ for even $n$. We classify uniform rank $n$ bundles on ${\mathbb{Q}}^n$ for $n=3$, $5$. Furthermore, we characterize projective spaces among generalized Grassmannians in terms of uniform bundles.

27 pages