Taut foliations in branched cyclic covers and left-orderable groups

TL;DR

This paper investigates the relationship between taut foliations and left-orderability of fundamental groups in cyclic branched covers of links, proving new cases of the L-space conjecture and establishing properties of universal abelian covers.

Contribution

It proves the L-space conjecture for certain 3-manifolds and shows that universal abelian covers of surgeries on hyperbolic fibred knots admit taut foliations and have left-orderable groups.

Findings

Confirmed the L-space conjecture for specific 3-manifolds with genus 1 fibred knots.

Established that universal abelian covers of certain surgeries admit taut foliations.

Proved the Euler class of a universal circle representation matches that of the foliation's tangent bundle.

Abstract

We study the left-orderability of the fundamental groups of cyclic branched covers of links which admit co-oriented taut foliations. In particular we do this for cyclic branched covers of fibred knots in integer homology $3$-spheres and cyclic branched covers of closed braids. The latter allows us to complete the proof of the L-space conjecture for closed, connected, orientable, irreducible $3$-manifolds containing a genus $1$ fibred knot. We also prove that the universal abelian cover of a manifold obtained by generic Dehn surgery on a hyperbolic fibred knot in an integer homology $3$-sphere admits a co-oriented taut foliation and has left-orderable fundamental group, even if the surgered manifold does not, and that the same holds for many branched covers of satellite knots with braided patterns. A key fact used in our proofs is that the Euler class of a universal circle representation associated to a co-oriented taut foliation coincides with the Euler class of the foliation's tangent bundle. Though known to experts, no proof of this important result has appeared in the literature. We provide such a proof in the paper.