On some natural torsors over moduli spaces of parabolic bundles

Abstract

A moduli space ${\mathcal N}$ of stable parabolic vector bundles, of rank $r$ and parabolic degree zero, on a $n$-pointed curve has two naturally occurring holomorphic $T^*{\mathcal N}$--torsors over it. One of them is given by the moduli space of pairs of the form $(E_*, D)$, where $E_* \in {\mathcal N}$ and $D$ is a connection on $E_*$. This $T^*{\mathcal N}$--torsor has a $C^\infty$ section that sends any $E_* \in {\mathcal N}$ to the unique connection on it with unitary monodromy. The other $T^*{\mathcal N}$--torsor is given by the sheaf of holomorphic connections on a theta line bundle over ${\mathcal N}$. This $T^*{\mathcal N}$--torsor also has a $C^\infty$ section given by the Hermitian structure on the theta bundle constructed by Quillen. We prove that these two $T^*{\mathcal N}$--torsors are isomorphic by a canonical holomorphic map. This holomorphic isomorphism interchanges the above two $C^\infty$ sections.