Restricted Marstrand projection conjecture for analytic families

Let Pt:RnRmP_t:\mathbb{R}^n\rightarrow\mathbb{R}^m be an analytic family of linear maps, meaning that its coordinate functions are analytic functions of tt. Assume that for every subspace π\pi of Rn\mathbb{R}^n, one has

dimPt(π)=min(dimπ,m)\dim P_t(\pi)=\min(\dim\pi,m)

for all but finitely many t[0,1]t\in[0,1]. Restricted Marstrand's conjecture. For every Borel set ARnA\subset\mathbb{R}^n,

dimHPt(A)=min(dimHA,m)\dim_H P_t(A)=\min(\dim_H A,m)

for almost every t[0,1]t\in[0,1]. This conjecture asserts that failure of the restricted Marstrand projection theorem should already be detected by a subspace. It generalizes the expected almost-everywhere Hausdorff-dimension formula from classical projection theory to analytic families of linear maps.

Sources & referencesView supporting material

Primary source

Jiahan Du, “Restricted Marstrand's projection theorem for general families of linear subspaces”, arXiv:2510.16671 (2025).

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