The general Frobenius decomposition conjecture for flag varieties

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Let n∈Nn\in\mathbb N. Define subcategories of Db(Xn)\mathop{\mathrm D\kern0pt}\nolimits^b(X_n) by

A=⟨Ak⟩,0<k≤n−1,\mathcal A=\langle\mathcal A_k\rangle,\qquad 0<k\leq n-1,

with A0=⟨OXn⟩\mathcal A_0=\langle\mathcal O_{X_n}\rangle, and for k<0k<0 let Ak\mathcal A_k be defined inductively as the left mutation of the subcategory generated by Liω1+(k−i)ωn−1\mathcal L_{i\omega_1+(k-i)\omega_{n-1}} for 0≤i≤k0\leq i\leq k through the subcategory generated by Al\mathcal A_l for 0≤l<k0\leq l<k. Let

B=⟨ΛiE⊗L−ω1⟩,0≤i≤n−2,\mathcal B=\langle\Lambda^i\mathcal E\otimes\mathcal L_{-\omega_1}\rangle,\qquad 0\leq i\leq n-2,

and define A~=⟨A~k⟩\widetilde{\mathcal A}=\langle\widetilde{\mathcal A}_k\rangle for −n+2<k≤0-n+2<k\leq0, where A~0=⟨L−ω1−ωn⟩\widetilde{\mathcal A}_0=\langle\mathcal L_{-\omega_1-\omega_n}\rangle, and for k<0k<0, A~k\widetilde{\mathcal A}_k is the right mutation of the subcategory generated by L(−k+i)ω1−iωn−1⊗L−ω1−ωn\mathcal L_{(-k+i)\omega_1-i\omega_{n-1}}\otimes\mathcal L_{-\omega_1-\omega_n} for 0≤i≤−k0\leq i\leq-k through the subcategory generated by A~l\widetilde{\mathcal A}_l for k<l≤0k<l\leq0. The general Frobenius decomposition conjecture. The collection

⟨A~,B,A⟩\langle\widetilde{\mathcal A},\mathcal B,\mathcal A\rangle

is a semiorthogonal decomposition of Db(Xn)\mathop{\mathrm D\kern0pt}\nolimits^b(X_n) satisfying the conditions of Theorem, and the indecomposable summands of F∗OXn{\sf F}_*\mathcal O_{X_n} are the terms of the right dual decomposition to this semiorthogonal decomposition. This conjecture extrapolates the decompositions established in the preceding low-rank cases to general nn and predicts the indecomposable summands of the Frobenius pushforward.

References

Primary source

Alexander Samokhin, “The Frobenius morphism on flag varieties, II”, arXiv:1705.10187 (2017).

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