Splitting the mapping class group extension for connected sums of equal-dimensional sphere products

Determine whether the exact sequence relating the Torelli group, the mapping class group, and the group G_g splits for the connected sum of g copies of S^p × S^p when g = 1 and p = 7.

Background

The paper compares its mapping class group calculations for connected sums of Sp × S{p+1} with known results for connected sums of Sp × Sp. For odd p, prior work establishes nonsplitting for g ≥ 2 and splitting for g = 1 except when p = 3 or 7. The remaining case g = 1, p = 7 is explicitly identified as unresolved.

References

For $g = 1$, when $p = 3$ it does not split by , and the case $p = 7$ is open.

Mapping class groups of simply connected closed spin 5-manifolds with no 2- and 3-torsion in homology  (2608.26698 - Jin, 27 Aug 2026) in Remark in Section 1.1, item (3)