Nicholas McConnell's REU 2020 Web Page

About Me

Name: Nicholas McConnell
Email: ncm78 (at)
Office: N/A
Home Institution: Rutgers University
Project: Heegaard-Floer homology and knot theory
Mentor: Kristen Hendricks

About My Project

My project is tied around knot theory and Heegaard-Floer homology. It starts out involving some basic homological algebra, along with the core concept of knots in S3.

The goal of the summer research project is to study the Heegaard-Floer homology of knots and related knot invariants, to get a good view of their topological distinctions.

This website is sponsored by NSF Grant DMS-2019396 and the Rutgers University Mathematics Department.

Research Log

Week 1

This week, I read Peter Ozsvath's text on Heegaard's decompositions, and studied the knot groups for certain knots in general, using the Mayer-Vietoris sequence. Then I read Ciprian Manolescu's paper on knot Floer homology to get a better idea of what things are like.

Week 2

I got better knowledge of how Heegaard decompositions of S3 can be represented in a way to indicate a specific knot, and how to use these indications to get the complex CFK.

Week 3

The figure-8 knot's Heegaard-Floer homology was covered, along with the Sarkar involution and the map \iotak.

Week 4

Further studies of the Heegaard-Floer homology, particularly of 10161. Will start thinking about the pretzel knot P(-2,m,k) with m and k odd.

Week 5

This week, we learned how to derive the CFK complex for the pretzel knot P(-2,m,k), and worked out \iotak in a few special cases. This approaches the goal of the REU project.

Week 6

We studied thin knots, and the specific properties they have (e.g., the lack of nonzero filtered chain homotopies).

Week 7

This week, I looked at my mentor's paper on the subject. It covered the diagrams for a few example knots, such as the figure 8 knot. One can generally do similar things for the pretzel knot.

Our paper intends to be about general formulas for the homology of pretzel knots.

Week 8

Focused on changing basis in certain examples, and proving the main lemmas for pretzel knots: The \iotak exchanges the filtration gradings (i,j) and (j,i). Also, there is no nonzero filtered map (even if it does not need to be a chain map) which sends homological grading s to s+1, hence homotopic maps such as \iotak2 and the Sarkar involution must be equal.

Week 9

This was the final week of the REU, with the presentations Wednesday-Friday. Me and my co-worker Matthew Isaac have presented our project at 11 AM.

References & Links

Here are the papers I have read for my project:
  1. Knot Floer homology of (1,1)-knots, Hiroshi Goda, Hiroshi Matsuda, and Takayuki Morifuji - Geom. Dedicata 112 (2005), 197-214. MR 2163899
  2. Involutive Heegaard Floer homology, Kristen Hendricks and Ciprian Manolescu - Duke Math. J. 166 (2017), no. 7, 1211-1299.
  3. An Introduction to Knot Floer Homology, Ciprian Manolescu - Retrieved from here.
  4. An introduction to Heegaard Floer homology, Peter Ozsváth and Zoltán Szabó - Retrieved from here.
  5. Algebraic Topology, Allen Hatcher - Retrieved from here.
Here is my mentor's website, and the REU website: