Satellite knots and immersed Heegaard Floer homology

TL;DR

This paper introduces a new, more efficient method for computing the knot Floer complex of satellite knots using immersed Heegaard diagrams, simplifying previous bordered Floer techniques especially for genus one patterns.

Contribution

It develops an immersed curve approach to compute the $UV=0$ knot Floer complex of satellite knots from pattern and companion data, extending previous methods and handling immersed diagrams.

Findings

The method simplifies computations for satellite knots.

It generalizes previous work for (1,1) patterns.

The approach is often more computationally feasible.

Abstract

We describe a new method for computing the $UV = 0$ knot Floer complex of a satellite knot given the $UV = 0$ knot Floer complex for the companion and a doubly pointed bordered Heegaard diagram for the pattern, showing that the complex for the satellite can be computed from an immersed doubly pointed Heegaard diagram obtained from the Heegaard diagram for the pattern by overlaying the immersed curve representing the complex for the companion. This method streamlines the usual bordered Floer method of tensoring with a bimodule associated to the pattern by giving an immersed curve interpretation of that pairing, and computing the module from the immersed diagram is often easier than computing the relevant bordered bimodule. In particular, for (1,1) patterns the resulting immersed diagram is genus one, and thus the computation is combinatorial. For (1,1) patterns this generalizes previous work of the first author which showed that such immersed Heegaard diagram computes the $V=0$ knot Floer complex of the satellite. As a key technical step, which is of independent interest, we extend the construction of a bigraded complex from a doubly pointed Heegaard diagram and of an extended type D structure from a torus-boundary bordered Heegaard diagram to allow Heegaard diagrams containing an immersed alpha curve.