Georgia Institute of Technology College of Sciences

In this talk, we will give background on Lefschetz fibrations and their relationship to symplectic 4-manifolds. We will then discuss results on their fundamental groups. Genus-2 Lefschetz fibrations are of particular interest because of how much we know and don't know about them. We will see what fundamental groups a genus-2 Lefschetz fibration can have and what questions someone might ask when studying these objects.

Let P be a set of points and L be a set of lines in the plane, what can we say about the number of incidences between P and L,    I(P, L):= |\{ (p, l)\in P\times L, p\in L\}| ?

The problem changes drastically when we consider a thickening version, i.e. when P is a set of unit balls and L is a set of tubes of radius 1. Furstenberg set conjecture can be viewed as an incidence problem for tubes. It states that a set containing an s-dim subset of a line in every direction should have dimension at least  (3s+1)/2 when s>0. 

We will survey a sequence of results by Orponen, Shmerkin and a recent joint work with Ren that leads to the solution of this conjecture