Partial-transposition conjecture for pillar entries of Schubert tangent cones

Let SnS_n be the symmetric group, let w,winSnw,w'in S_n, and let r(w)r(w) and r(w)r(w') be their rank matrices. Write Tw\mathcal{T}_w for the tangent cone of the Schubert variety associated with ww, and call an entry of a rank matrix a pillar entry in the sense of the paper. A partial transposition matches pillar entries while either preserving their positions or transposing their positions.

Partial-transposition conjecture. If

Tw=Tw,\mathcal{T}_w=\mathcal{T}_{w'},

then the rank matrices r(w)r(w) and r(w)r(w') have the same number of pillar entries, and for every pillar entry rijr_{ij} of r(w)r(w), either rijr'_{ij} is a pillar entry with rij=rijr'_{ij}=r_{ij}, or rjir'_{ji} is a pillar entry with rji=rijr'_{ji}=r_{ij}.

The conjecture proposes that equal tangent cones are detected by matching pillar entries up to independent transpositions. Its converse is false, while the stated implication was disproved by examples in the source.

Sources & referencesView supporting material

Primary source

Dmitry Fuchs, Alexandre Kirillov, Sophie Morier-Genoud and Valentin Ovsienko, “On tangent cones of Schubert varieties”, arXiv:1606.07846 (2017).

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