Algebraic surfaces with $p_g=q=1, K^2=4$ and nonhyperelliptic Albanese fibrations of genus 4

TL;DR

This paper constructs and classifies a family of minimal algebraic surfaces with specific invariants and nonhyperelliptic Albanese fibrations of genus 4, showing they form a significant irreducible component of the moduli space.

Contribution

It constructs the first explicit family of such surfaces as complete intersections in a P^3-bundle over an elliptic curve and characterizes all similar surfaces with decomposable canonical sheaf images.

Findings

Constructed a family of surfaces as (2,3) complete intersections in a P^3-bundle.

Proved all surfaces with certain properties are contained in this family.

Identified a 4-dimensional irreducible component of the moduli space.

Abstract

In this paper we study minimal algebraic surfaces with $p_g=q=1,K^2=4$ and nonhyperelliptic Albanese fibrations of genus 4. We construct for the first time a family of such surfaces as complete intersections of type $(2,3)$ in a $\mathbb{P}^3$-bundle over an elliptic curve. For the surfaces we construct here, the direct image of the canonical sheaf under the Albanese map is decomposable (which is a topological invariant property). Moreover we prove that, all minimal surfaces with $p_g=q=1,K^2=4$ and nonhyperelliptic Albanese fibrations of genus 4 such that the direct image of the canonical sheaf under the Albanese map is decomposable are contained in our family. As a consequence, we show that these surfaces constitute a 4-dimensional irreducible subset $\mathcal{M}$ of $\mathcal{M}_{1,1}^{4,4}$, the Gieseker moduli space of minimal surfaces with $p_g=q=1, K^2=g=4$. Moreover, the closure of $\mathcal{M}$ is an irreducible component of $\mathcal{M}_{1,1}^{4,4}$.