Geography of Genus 2 Lefschetz fibrations

Kai Nakamura

Published 2018-11-08Version 1

Questions of geography of various classes of $4$-manifolds have been a central motivating question in $4$-manifold topology. Baykur and Korkmaz asked which small, simply connected, minimal $4$-manifolds admit a genus $2$ Lefschetz fibration. They were able to classify all the possible homeomorphism types and realize all but one with the exception of a genus $2$ Lefschetz fibration on a symplectic $4$-manifold homeomorphic, but not diffeomorphic to $3 \mathbb{CP}^2 \# 11\overline{\mathbb{CP}}^2$. We give a positive factorization of type $(10,10)$ that corresponds to such a genus $2$ Lefschetz fibration. Furthermore, we observe two restrictions on the geography of genus $2$ Lefschetz fibrations, we find that they satisfy the Noether inequality and a BMY like inequality. We then find positive factorizations that describe genus $2$ Lefschetz fibrations on simply connected, minimal symplectic $4$-manifolds for many of these points.