Robert Harris, University of Waterloo
Exotic constructions on covers branched over hyperplane arrangements
As a consequence of embedded surfaces and codimension two submanifolds coinciding in dimension four, many of the tools that are used in higher dimensions fail or are underwhelming when applied to 4-manifolds. For this reason, the development and advancement of techniques that are applicable to 4-manifolds are of particular interest and importance to low dimensional topologists. The general techniques of interest are those that either construct a 4-manifold in a novel way or those that provide ample control over the geometric data of the resulting 4-manifold.
In this talk, I will discuss my thesis, in which we investigate ways to construct 4-manifolds with positive signature. We also describe a construction that can guarantee the existence of algebraically interesting embedded symplectic submanifolds.
Specifically, we discuss how the combinatorial data of line arrangements and the algebraic data of their complements in rational complex surfaces can be utilized to construct symplectic 4-manifolds with arbitrarily large signatures through the method of branched coverings. In general, we not only show that these line arrangements can be used to provide asymptotic bounds for the existence of symplectic 4-manifolds but we also show that for any line arrangement, there exists symplectic branched covers with sufficiently nice geometric and topological properties. Namely, we show they contain embedded symplectic Riemann surfaces which carry their fundamental group.
Online presentation: contact r26harri@uwaterloo.ca for details on how to attend