Relations between Reeb graphs, systems of hypersurfaces and epimorphisms onto free groups

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Hauptverfasser: Marzantowicz, Wacław, Michalak, Łukasz Patryk
Format: Preprint
Veröffentlicht: 2020
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author Marzantowicz, Wacław
Michalak, Łukasz Patryk
author_facet Marzantowicz, Wacław
Michalak, Łukasz Patryk
contents We construct a correspondence between epimorphisms $φ\colon π_1(M) \to F_r$ from the fundamental group of a compact manifold $M$ onto the free group of rank $r$, and systems of $r$ framed non-separating hypersurfaces in $M$, which induces a bijection onto framed cobordism classes of such systems. In consequence, for closed manifolds any such $φ$ can be represented by the Reeb epimorphism of a Morse function $f\colon M \to \mathbb{R}$, i.e. by the epimorphism induced by the quotient map $M \to \mathcal{R}(f)$ onto the Reeb graph of $f$. Applying this construction we discuss the problem of classification up to (strong) equivalence of epimorphisms onto free groups, providing a new purely geometrical-topological proof of the solution of this problem for surface groups.
format Preprint
id arxiv_https___arxiv_org_abs_2002_02388
institution arXiv
publishDate 2020
record_format arxiv
spellingShingle Relations between Reeb graphs, systems of hypersurfaces and epimorphisms onto free groups
Marzantowicz, Wacław
Michalak, Łukasz Patryk
Geometric Topology
Group Theory
20F65 (Primary), 57M15, 57R90 (Secondary)
We construct a correspondence between epimorphisms $φ\colon π_1(M) \to F_r$ from the fundamental group of a compact manifold $M$ onto the free group of rank $r$, and systems of $r$ framed non-separating hypersurfaces in $M$, which induces a bijection onto framed cobordism classes of such systems. In consequence, for closed manifolds any such $φ$ can be represented by the Reeb epimorphism of a Morse function $f\colon M \to \mathbb{R}$, i.e. by the epimorphism induced by the quotient map $M \to \mathcal{R}(f)$ onto the Reeb graph of $f$. Applying this construction we discuss the problem of classification up to (strong) equivalence of epimorphisms onto free groups, providing a new purely geometrical-topological proof of the solution of this problem for surface groups.
title Relations between Reeb graphs, systems of hypersurfaces and epimorphisms onto free groups
topic Geometric Topology
Group Theory
20F65 (Primary), 57M15, 57R90 (Secondary)
url https://arxiv.org/abs/2002.02388