Finite-codimension criterion for finite determinacy in positive characteristic

Let KK be the ground field, let R=K[[x1,,xs]]R=K[[x_1,\ldots,x_s]] with maximal ideal m\mathfrak{m}, and let AmMm,nA\in\mathfrak{m}\cdot M_{m,n} be a matrix. Let GG act on Mm,nM_{m,n} by the equivalence considered in the paper, and let T~A(GA)\widetilde T_A(GA) denote the tangent image at AA to the orbit GAGA. Finite KK-codimension of T~A(GA)\widetilde T_A(GA) means that Mm,n/T~A(GA)M_{m,n}/\widetilde T_A(GA) is finite-dimensional over KK. The conjecture. Statement 2 of the cited theorem should hold also when char(K)>0\operatorname{char}(K)>0: the condition that there exists an integer k0k\geq 0 such that

mk+2Mm,nmT~A(GA)\mathfrak{m}^{k+2}\cdot M_{m,n}\subset \mathfrak{m}\cdot\widetilde T_A(GA)

should be equivalent to AA being finitely GG-determined. In positive characteristic, this asserts in particular that finite codimension of the tangent image is necessary for finite GG-determinacy. The theorem establishes this equivalence in characteristic zero, while the source explicitly states that its validity in positive characteristic is unknown; the tangent image can be strictly smaller than the tangent space there.

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Primary source

Gert-Martin Greuel and Thuy Huong Pham, “Finite determinacy of matrices and ideals”, arXiv:1708.02442 (2019).

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