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BNS INVARIANTS AND ALGEBRAIC FIBRATIONS OF GROUP EXTENSIONS

Part of: Low-dimensional topology

Published online by Cambridge University Press:  21 September 2021

Stefan Friedl  and
Stefano Vidussi Open the ORCID record for Stefano Vidussi [Opens in a new window]
Stefan Friedl
Affiliation:
Fakultät für Mathematik, Universität Regensburg, Germany ([email protected])
Stefano Vidussi
Affiliation:
Fakultät für Mathematik, Universität Regensburg, Germany ([email protected]) Department of Mathematics, University of California, Riverside, CA 92521, USA ([email protected])
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Abstract

Let G be a finitely generated group that can be written as an extension

$$ \begin{align*} 1 \longrightarrow K \stackrel{i}{\longrightarrow} G \stackrel{f}{\longrightarrow} \Gamma \longrightarrow 1 \end{align*} $$
where K is a finitely generated group. By a study of the Bieri–Neumann–Strebel (BNS) invariants we prove that if $b_1(G)> b_1(\Gamma ) > 0$ , then G algebraically fibres; that is, admits an epimorphism to $\Bbb {Z}$ with finitely generated kernel. An interesting case of this occurrence is when G is the fundamental group of a surface bundle over a surface $F \hookrightarrow X \rightarrow B$ with Albanese dimension $a(X) = 2$ . As an application, we show that if X has virtual Albanese dimension $va(X) = 2$ and base and fibre have genus greater that $1$ , G is noncoherent. This answers for a broad class of bundles a question of J. Hillman ([9, Question 11(4)]). Finally, we show that there exist surface bundles over a surface whose BNS invariants have a structure that differs from that of Kodaira fibrations, determined by T. Delzant.

Keywords

Algebraic fibrationsgroups extensionsBieri-Neumann-Strebel invariants

MSC classification

Primary: 57M07: Topological methods in group theory
Type
Research Article
Information
Journal of the Institute of Mathematics of Jussieu , Volume 22 , Issue 2 , March 2023 , pp. 985 - 999
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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