On the components of the Main Stream of the moduli space of surfaces of general type with $p_g=q=2$

TL;DR

This paper constructs and classifies specific families of surfaces of general type with invariants p_g=q=2, describing their moduli space components and answering questions about their Albanese maps and Tschirnhaus modules.

Contribution

It provides explicit constructions of moduli space components for surfaces with p_g=q=2, including new families and answers to open questions about Albanese maps and Tschirnhaus modules.

Findings

Constructed the CHPP family with p_g=q=2, K^2=5, Albanese degree 3.

Constructed the PP4 family with p_g=q=2, K^2=6, Albanese degree 4.

Answered a question by Chen and Hacon about Tschirnhaus modules with nontrivial homogeneous bundle quotients.

Abstract

We give first an easy construction of surfaces with $p_g=q=2, K^2=5$ and Albanese map of degree $3$, describing an irreducible connected component of the moduli space of surfaces of general type, which we show to be the only one of the Main Stream with these invariants and satisfying a mild condition. We call it the family of CHPP surfaces, since it contains the family constructed by Chen and Hacon, and coincides with the one considered by Penegini and Polizzi. We also give an easy construction of an irreducible connected component of the moduli space of surfaces of general type with $p_g=q=2, K^2=6$ and Albanese map of degree $4$, which we call the family of PP4 surfaces since it contains the family constructed by Penegini and Polizzi. Finally, we answer a question posed by Chen and Hacon, via three families of surfaces with $p_g=q$ whose Tschirnhaus module has a kernel realization with quotient a nontrivial homogeneous bundle. Two families have $p_g=q=3$, the third is a new family of surfaces with $p_g=q=2, K^2=6$ and Albanese map of degree $3$ (the existence of this family is based on arXiv:2212.14877, joint work of the second author with Edoardo Sernesi) .