On the classification of fine compactified Jacobians of nodal curves

TL;DR

This paper introduces a new, larger class of fine compactified Jacobians for nodal curves, called fine V-compactified Jacobians, which generalize previous models and are characterized by their deformation and combinatorial properties.

Contribution

The paper defines fine V-compactified Jacobians, characterizes them via limits of smooth Jacobians, and provides a combinatorial description based on orbit posets.

Findings

Fine V-compactified Jacobians include and extend classical models.

They can be obtained as limits of Jacobians under smoothing.

They provide a compactification of the Néron model.

Abstract

We introduce a new class of fine compactified Jacobians for nodal curves, that we call fine compactified Jacobians of vine type, or simply fine V-compactified Jacobians. This class is strictly larger than the class of fine classical compactified Jacobians, as constructed by Oda-Seshadri, Simpson, Caporaso and Esteves. Inspired by a recent preprint of Pagani-Tommasi, we characterize fine V-compactified Jacobians as the fine compactified Jacobians that can arise as limits of Jacobians of smooth curves under a one-parameter smoothing of the nodal curve or in its semiuniversal deformation space. Furthermore, fine V-compactified Jacobians are exactly the ones that gives a compactification of the N\'eron model of the Jacobian of the generic fiber of a one-parameter regular smoothing of the nodal curve. Finally, we give a combinatorial characterization of fine V-compactified Jacobians in terms of their poset of orbits for the action of the generalized Jacobian.