Segre invariant and a stratification of the moduli space of coherent systems

Abstract

The aim of this paper is to generalize the $m-$Segre invariant for vector bundles to coherent systems. Let $X$ be a non-singular irreducible complex projective curve of genus $g$ over $\mathbb{C}$ and $(E,V)$ be a coherent system on $X$ of type $(n,d,k)$. For any pair of integers $m,t$, $0<m<n$, $0\le t\le k$ we define the $(m,t)-$Segre invariant, denoted by $S_{m,t}^{\alpha }$ and show that $S_{m,t}^{\alpha }$ induces a semicontinuous function on the families of coherent systems. Thus, $S_{m,t}^{\alpha }$ gives a stratification of the moduli space $G(\alpha ;n,d,k)$ of $\alpha -$stable coherent systems of type $(n,d,k)$ on $X$ into locally closed subvarieties $G(\alpha ;n,d,k;m,t;s)$ according to the value $s$ of $S_{m,t}^{\alpha }$. We study the stratification, determine conditions under which the different strata are non-empty and compute their dimension.

References in corpus (1)

• On linear systems and a conjecture of D. C. Butler