The general Frobenius decomposition conjecture for flag varieties

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

A=Ak,0<kn1,\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+(ki)ωn1\mathcal L_{i\omega_1+(k-i)\omega_{n-1}} for 0ik0\leq i\leq k through the subcategory generated by Al\mathcal A_l for 0l<k0\leq l<k. Let

B=ΛiELω1,0in2,\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<k0-n+2<k\leq0, where A~0=Lω1ωn\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)ω1iωn1Lω1ωn\mathcal L_{(-k+i)\omega_1-i\omega_{n-1}}\otimes\mathcal L_{-\omega_1-\omega_n} for 0ik0\leq i\leq-k through the subcategory generated by A~l\widetilde{\mathcal A}_l for k<l0k<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 FOXn{\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.

Sources & referencesView supporting material

Primary source

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

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