Corks, Concordance, and Complex Curves

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Differential topology is concerned with manifolds — objects such as circles, spheres, and tori (and their higher-dimensional analogs). Manifolds arise naturally in physics (our universe as a 4-dimensional manifold), computer science (graphics), and biology (investigating how the shape and "knottedness" of molecules like DNA affect their function). In many ways, this subject is especially interesting for 4-dimensional spaces. Fortunately, a manifold can often be studied using the lower-dimensional manifolds that sit inside of it. Remarkably, several of the most important questions about 4-dimensional manifolds can be reduced to asking if a given knotted circle in 3-space arises as the boundary of a 2-dimensional disk in 4-space. This project aims to develop new techniques to tackle this latter problem and related questions, with a range of applications in 4-dimensional topology. Of particular interest are the disks and surfaces in 4-space that arise as solution sets to equations with two complex variables, known as "complex plane curves". Such surfaces exhibit surprising connections to foundational questions about 4-manifolds, as well as connections to other areas of mathematics, such as the mathematical theory of braids. In addition, aspects of the project aim to illuminate the connections between complex plane curves and important topological tools that have deep connections to mathematical physics. These projects include accessible entry points for undergraduate research.The project is guided by three interrelated questions: (1) When does a knot in 3-space bound a disk (or another low-genus surface) in 4-space? (2) How unique is an embedded surface in a 4-manifold, up to isotopy? (3) Which smooth surfaces in complex manifolds are isotopic to complex curves? For all three questions, the PI aims to blend constructive techniques (such as handle calculus and branched coverings) to enhance the power of obstructive tools like Heegaard Floer homology and Khovanov homology. Further investigation of the cobordism maps in the aforementioned homology theories will help shed light on whether these tools can be used to detect pairs of orientable surfaces in 4-dimensional space that are "exotically knotted", i.e., isotopic through ambient homeomorphisms but not diffeomorphisms. In particular, the PI will use these homology theories to investigate uniqueness problems for complex curves. In addition, the PI will continue to develop topological techniques for studying complex curves in 4-space and other 4-manifolds, including novel techniques using singular foliations inspired by the theory of characteristic foliations in contact geometry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.