New examples of reducible theta divisors for some Syzygy bundles

Abstract

Let $C$ be a smooth complex irreducible projective curve of genus $g$ with general moduli, and let $(L,H^0(L))$ be a generated complete linear series of type $(d,r+1)$ over $C$. The syzygy bundle, denoted by $M_L$, is the kernel of the evaluation map $H^0(L)\otimes {\mathcal{O}}_C\to L$. In this work we have a double purpose. The first one is to give new examples of stable syzygy bundles admitting theta divisor over general curves. We prove that if $M_L$ is strictly semistable then $M_L$ admits reducible theta divisor. The second purpose is to study the cohomological semistability of $M_L$, and in this direction we show that when $L$ induces a birational map, the syzygy bundle $M_L$ is cohomologically semistable, and we obtain precise conditions for the cohomological semistability of $M_L$ where such conditions agree with the semistability conditions for $M_L$.

10 pages. Remove Lemma 2.5 and Theorem 2.7 related with the not injectivity of the theta map

References in corpus (2)

• Generalized theta linear series on moduli spaces of vector bundles on curves
• Linear stability and stability of Lazarsfeld-Mukai bundles