Galashin–Lam's deformation-retract and filtration conjecture for open positroid varieties

Let kk and nn be coprime positive integers, let Xk,nX^\circ_{k,n} denote the top-dimensional open positroid variety, and let Jk,nkJ_{k,n-k} be the compactified Jacobian of the plane curve singularity xk=ynkx^k=y^{n-k}. A deformation retract is understood in the topological sense, without requiring it to be algebraic.

Galashin–Lam's conjecture. There exists a non-algebraic deformation retract

r:Xk,nJk,nkr:X^\circ_{k,n}\to J_{k,n-k}

from Xk,nX^\circ_{k,n} onto Jk,nkJ_{k,n-k}. Moreover, in compactly supported cohomology,

r:Hc(Jk,nk)Hc(Xk,n)r^*:H_c^*(J_{k,n-k})\to H_c^*(X^\circ_{k,n})

sends the weight filtration to the perverse filtration.

This conjecture connects the topology and filtrations of the open positroid variety with those of the compactified Jacobian of a plane curve singularity. The supplied text attributes the motivation to work of Galashin–Lam and to the works cited as STZ17 and STWZ19, but gives no resolution status.

Sources & referencesView supporting material

Primary source

Calvin Yost-Wolff, “Point Count of the Top-dimensional Open Positroid Variety”, arXiv:2602.15316 (2026).

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