Explicit adjoint formulas for parabolic Soergel bimodule categories

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Let (W,S)(W,S) be a Coxeter system, let I⊂SI\subset S, and let h\mathfrak{h} be a realization of WW with fundamental weights {ρs}s∈S\{\rho_s\}_{s\in S}. Write {s1,…,sℓ}\{s_1,\ldots,s_\ell\} for the complement of II in SS. Let πL\pi_L and πR\pi_R be the left and right adjoints to the inclusion

Kb(SBim⁡(h,WI))⟶Kb(SBim⁡(h,W)).K^b(\mathbb{S}\operatorname{Bim}(\mathfrak{h},W_I))\longrightarrow K^b(\mathbb{S}\operatorname{Bim}(\mathfrak{h},W)).

Explicit adjoint formulas conjecture. The adjoints satisfy

πL≅πs1+∘⋯∘πsℓ+,πR≅πs1−∘⋯∘πsℓ−.\pi_L\cong \pi^+_{s_1}\circ\cdots\circ\pi^+_{s_\ell},\qquad \pi_R\cong \pi^-_{s_1}\circ\cdots\circ\pi^-_{s_\ell}.

These formulas are independent of the order chosen for the complement of II in SS. The conjecture gives an explicit description of the adjoints whose existence is known in general, but the asserted formulas and order-independence remain open.

References

Primary source

Cailan Li, “Serre Duality and the Whitehead Link”, arXiv:2509.22133 (2025).

Additional references

3 papers in this index state this conjecture (2007–2025). The statement above is taken from the most recent of them; the others are arXiv:1807.02945, arXiv:0710.0960.

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