Cubiquitous lattices and branched covers bounding rational balls

In [8], Greene and Owens explore cubiquitous lattices as an obstruction to rational homology 3-spheres bounding rational homology 4-balls. The purpose of this article is to better understand which sublattices of ℤ n are cubiquitous with the aim of effectively using their cubiquity obstruction. We develop a geometric obstruction (called the Wu obstruction) to cubiquity and use it as tool to completely classify which sublattices with orthogonal bases are cubiquitous. We then apply this result to the double branched covers of alternating connected sums of torus links. Finally, we explore how the Wu obstruction can be used in conjunction with contractions to obstruct the cubiquity of infinite families of lattices.