Polynomial dimension conjecture for multiplicatively invariant sets

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Fix n,m∈Nn,m\in\mathbb{N} and let

Δ(A,B)={an+bm∣a∈A,b∈B}\Delta(A,B)=\{a^n+b^m\mid a\in A,b\in B\}

for A,B⊆N0A,B\subseteq\mathbb{N}_0. Let r,s∈Nr,s\in\mathbb{N} be multiplicatively independent, and let A,B⊆N0A,B\subseteq\mathbb{N}_0 be ×r\times r- and ×s\times s-invariant subsets, respectively. Polynomial dimension conjecture. One has

dim⁡M⁡Δ(A,B)=min⁡(1ndim⁡M⁡A+1mdim⁡M⁡B,1).\dim_{\operatorname{M}}\Delta(A,B)=\min\left(\frac{1}{n}\dim_{\operatorname{M}} A+\frac{1}{m}\dim_{\operatorname{M}} B,1\right).

This is a special case of a natural polynomial extension of the dimension formula for sumsets of multiplicatively invariant sets. The conjecture was recently proved independently by Shmerkin and Wu.

References

Primary source

Daniel Glasscock, Joel Moreira and Florian K. Richter, “Additive and geometric transversality of fractal sets in the integers”, arXiv:2007.05480 (2025).

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