Classifying affine line bundles on a compact complex space

Abstract

The classification of affine line bundles on a compact complex space $X$ is a difficult problem. We study the affine analogue of the Picard functor and the representability problem for this functor. For a fixed Chern class $c$, we introduce the affine Picard functor $Picaff_{X,x_0}^c:An^{op}\to Set$ which assigns to a complex space $T$ the set of families of linearly $x_0$-framed affine line bundles on $X$ with Chern class $c$ parameterized by $T$. Our main result states that this functor is representable if and only if the map $h^0:Pic^c(X)\to\mathbb{N}$ is constant. If this is the case, the space which represents this functor is a linear space over $Pic^c(X)$ whose underlying set is $\coprod_{l\in Pic^c(X)} H^1(\mathcal{L}_{\{l\}\times X})$, where $\mathcal{L}$ is a Poincar\'e line bundle normalized at $x_0$. The main idea idea of the proof is to compare the representability of our functor to the representability of a functor considered by Bingener related to the deformation theory of $p$-cohomology classes. Our arguments show in particular that, for $p=1$, the converse of Bingener's representability criterion holds.