Generalized restricted Marstrand conjecture for analytic linear families

Let Pt:RnRmP_t:\mathbb{R}^n\rightarrow\mathbb{R}^m be an analytic family of linear maps. Define f:[0,n]Rf:[0,n]\rightarrow\mathbb{R} as follows: for an integer x[0,n]x\in[0,n], let f(x)f(x) be the largest integer such that every subspace ARnA\subset\mathbb{R}^n with dimA=x\dim A=x satisfies

dimPt(A)f(x)\dim P_t(A)\geq f(x)

for all but finitely many t[0,1]t\in[0,1]; for noninteger xx, define ff linearly on [x,x+1][\lfloor x\rfloor,\lfloor x\rfloor+1]. Generalized restricted Marstrand conjecture. For every Borel set ARnA\subset\mathbb{R}^n,

dimHPt(A)f(dimHA)\dim_H P_t(A)\geq f(\dim_H A)

for almost every t[0,1]t\in[0,1]. This is a more general lower-bound formulation of the restricted Marstrand problem, allowing the expected projection dimension to be determined by the eventual behavior of the family on subspaces.

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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