Recognition of the general type-(4,3) fundamental group as a torus-bundle group

Determine whether the fundamental group presented for the genus-3 Lefschetz pencil $X_\phi$ associated with an arbitrary matrix $\begin{pmatrix}p&q\\r&s\end{pmatrix}\in\mathrm{SL}(2,\mathbb{Z})$ can be recognized as the fundamental group of a torus bundle over a torus.

Background

For a general mapping class determined by a matrix in SL(2,Z)\mathrm{SL}(2,\mathbb{Z}), the paper gives a presentation for the fundamental group of the resulting pencil XϕX_\phi. In several special cases, the author identifies the group with the fundamental group of a torus bundle and consequently determines the homeomorphism type.

The remark explicitly records that the general presentation has not been recognized as a torus-bundle group. Resolving this question could extend the homeomorphism-type analysis from the computed special cases to the full family of type-(4,3)(4,3) constructions.

References

It is not clear to the author how to recognize this as the fundamental group of a torus bundle.

— Genus-3 Lefschetz pencils on torus bundles  (2610.06440 - Huang, 5 Oct 2026) in Section 6, Remark following Proposition on the pencils $X_k$