The conjectural restriction rule for completely splittable partitions

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Let λ\lambda be a completely splittable partition of height HH with χ(λ)=p\chi(\lambda)=p, and let α∈Zp\alpha\in\mathbb Z_p. Let AA be the top λ\lambda-addable node, namely the node in the first row. Suppose that λA\lambda^A has more than one normal node of residue α\alpha, and let BB be the bottom λ\lambda-removable node. Let x=[h2,1(λ)⩾p]x=[h_{2,1}(\lambda)\geqslant p] be the indicator of the stated inequality.

Restriction branching conjecture. Except for AA, the only λA\lambda^A-normal node of residue α\alpha is BB, and

[Res⁡αDλA]={2[Dλ~]+[Dλ]+[DH(−1,0H−3,1,0)(λ)]+x[DH(0,−1,0H−3,1)(λ)],H>2,2[Dλ~]+[Dλ]+x[DH(1,−1)(λ)],H=2.[\operatorname{Res}_\alpha D^{\lambda^A}]= \begin{cases} 2[D^{\tilde\lambda}]+[D^\lambda]+[D^{\mathcal H_{(-1,0^{H-3},1,0)}(\lambda)}]+x[D^{\mathcal H_{(0,-1,0^{H-3},1)}(\lambda)}],&H>2,\\ 2[D^{\tilde\lambda}]+[D^\lambda]+x[D^{\mathcal H_{(1,-1)}(\lambda)}],&H=2. \end{cases}

This is a proposed restriction-side branching formula, based on upper estimates and known decomposition matrices. The source supplies no proof or resolution status.

References

Primary source

Vladimir Shchigolev, “On extensions and branching rules for modules close to completely splittable”, arXiv:math/0408164 (2004).

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