# Taut foliations from double-diamond replacements

## TL;DR

This paper introduces a new sutured manifold decomposition called double-diamond taut and shows it guarantees the existence of co-oriented taut foliations for most boundary slopes in certain 3-manifolds, especially knot complements.

## Contribution

The paper defines double-diamond taut sutured manifold decompositions and proves their implications for taut foliations in 3-manifolds, including knot complements and Murasugi sums.

## Key findings

- Most boundary slopes are realized by taut foliations.
- Knot complements with certain surfaces are persistently foliar.
- Murasugi sums with even twists produce persistently foliar knots.

## Abstract

A 3-manifold is foliar if it supports a codimension-one co-oriented taut foliation. Suppose $M$ is an oriented 3-manifold with connected boundary a torus, and suppose $M$ contains a properly embedded, compact, oriented, surface $R$ with a single boundary component that is Thurston norm minimizing in $H_2(M, \partial M)$. We define a readily recognizable type of sutured manifold decomposition, which for notational reasons we call double-diamond taut, and show that if $R$ admits a double-diamond taut sutured manifold decomposition, then every boundary slope except one is strongly realized by a co-oriented taut foliation; that is, the foliation intersects $\partial M$ transversely in a foliation by curves of that slope. In the case that $M$ is the complement of a knot $\kappa$ in $S^3$, the exceptional filling is the meridional one, and hence $\kappa$ is persistently foliar, by which we mean that every non-trivial slope is strongly realized; hence, restricting attention to rational slopes, every manifold obtained by non-trivial Dehn surgery along $\kappa$ is foliar. In particular, if $R$ is a Murasugi sum of surfaces $R_1$ and $R_2$, where $R_2$ is an unknotted band with an even number $2m\ge 4$ of half-twists, then $\kappa= \partial R$ is persistently foliar.