Relative Serre duality conjecture for parabolic induction

Let (W,S)(W,S) be a Coxeter system, let I⊆SI\subseteq S be a subset of simple reflections, and let WIW_I be the parabolic subgroup generated by II. Let h\mathfrak{h} be a realization of WW, viewed also as a realization of WIW_I, and let

ι:Dm(h,WI)→Dm(h,W)\iota:D^m(\mathfrak{h},W_I)\to D^m(\mathfrak{h},W)

be the monoidal parabolic-induction functor, with left and right adjoints ιL\iota^L and ιR\iota^R. Let FT⁡W,I∈Dm(h,W)\operatorname{FT}_{W,I}\in D^m(\mathfrak{h},W) be the relative full twist defined using Rouquier's braid-group action. Relative Serre duality conjecture. If WW is finite, there are natural isomorphisms of functors

ιL(FT⁡W,I⋆−)≅ιR≅ιL(−⋆FT⁡W,I),\iota^L(\operatorname{FT}_{W,I}\star -)\cong\iota^R\cong\iota^L(-\star\operatorname{FT}_{W,I}),

and FT⁡W,I\operatorname{FT}_{W,I} naturally commutes under ⋆\star with objects of Dm(h,WI)D^m(\mathfrak{h},W_I). The conjecture was proved in the cited source, so the relative full twist describes both adjoints to parabolic induction and is central relative to the parabolic mixed derived category.

References

Primary source

Colton Sandvik, “Relative Serre duality for Coxeter groups”, arXiv:2604.06084 (2026).

Additional references

2 papers in this index state this conjecture (2025–2026). The statement above is taken from the most recent of them; the others are arXiv:2509.22133.

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