Conjecture on indecomposable summands of twisted Foulkes modules

From papers

Let H(2m;k)H^{(2^m;k)} denote the twisted Foulkes module for the symmetric group S2m+kS_{2m+k}. Let τ\tau be the pp-content and θ\theta the odd sequence of a partition of 2m+k2m+k, with k=θk=|\theta|. For a partition label τθ\tau-\theta, write Hτθ(2m)H^{(2^m)}_{\tau-\theta} for the corresponding summand of the Foulkes module, and let \boxtimes denote the outer tensor product, S2m+k\big\uparrow^{S_{2m+k}} induction to S2m+kS_{2m+k}, and (]τ(]_{\tau} projection to the block or pp-content τ\tau. Twisted Foulkes indecomposability conjecture. For all integers m,k0m,k\geq 0,

((Hτθ(2m)sgn)S2m+k)τ\left(\left(H^{(2^m)}_{\tau-\theta}\boxtimes\operatorname{sgn}\right)\big\uparrow^{S_{2m+k}}\right)_{\tau}

is indecomposable. Equivalently,

H(2m;k)=(τ,θ)((Hτθ(2m)sgn)S2m+k)τ,H^{(2^m;k)}=\bigoplus_{(\tau,\theta)}\left(\left(H^{(2^m)}_{\tau-\theta}\boxtimes\operatorname{sgn}\right)\big\uparrow^{S_{2m+k}}\right)_{\tau},

where the sum runs over all pairs (τ,θ)(\tau,\theta) arising from a partition of 2m+k2m+k with τ\tau its pp-content and θ\theta its odd sequence. This conjecture would give the decomposition of every twisted Foulkes module into indecomposable summands, extending the established decomposition for ordinary Foulkes modules. The source provides no resolution status.

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Sources & referencesView supporting material

Primary source

David J. Hemmer and Pavel Turek, “New columns in decomposition matrices of symmetric groups for every block”, arXiv:2606.28731 (2026).

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