# Persistently foliar composite knots

## TL;DR

This paper studies a special class of knots called persistently foliar knots, showing how this property is preserved under certain knot operations and providing methods to construct relevant foliations.

## Contribution

It proves that composite knots with persistently foliar summands are persistently foliar and introduces new foliation construction techniques involving branched surfaces.

## Key findings

- Composite knots with persistently foliar summands are persistently foliar.
- Connected sums of fibered knots are persistently foliar.
- Certain classes of composite knots are shown to be persistently foliar.

## Abstract

A knot $\kappa$ in $S^3$ is persistently foliar if, for each non-trivial boundary slope, there is a co-oriented taut foliation meeting the boundary of the knot complement transversely in a foliation by curves of that slope. For rational slopes, these foliations may be capped off by disks to obtain a co-oriented taut foliation in every manifold obtained by non-trivial Dehn surgery on that knot. We show that any composite knot with a persistently foliar summand is persistently foliar and that any nontrivial connected sum of fibered knots is persistently foliar. As an application, it follows that any composite knot in which each of two summands is fibered or at least one summand is nontorus alternating or Montesinos is persistently foliar. We note that, in constructing foliations in the complements of fibered summands, we build branched surfaces whose complementary regions agree with those of Gabai's product disk decompositions, except for the one containing the boundary of the knot complement. It is this boundary region which provides for persistence.