Furstenberg's dimension conjecture for multiplicatively independent orbits

Let pp and qq be two multiplicatively independent natural numbers, and let x[0,1)x\in[0,1) be a real number. Define the forward orbit

\mathcal O_q(x):=\left\\{x,T_q(x),T_q^2(x),\ldots\right\\},

where TqT_q is the map on R/Z\mathbb R/\mathbb Z given by xqxx\mapsto qx, and let dimH\dim_H denote Hausdorff dimension. Furstenberg's conjecture. Unless xx is rational,

dimHOp(x)+dimHOq(x)1.\dim_H \overline{\mathcal O_p(x)}+\dim_H \overline{\mathcal O_q(x)}\geq 1.

The conjecture expresses the expected trade-off between the complexity of expansions of an irrational real number in two multiplicatively independent bases. Shmerkin and Wu proved that the exceptional set has Hausdorff dimension zero, but the conjecture remains open in general.

Sources & referencesView supporting material

Primary source

Boris Adamczewski and Colin Faverjon, “Mahler's method in several variables and finite automata”, arXiv:2012.08283 (2020).

Additional references

2 papers in this index state this conjecture (2016–2020). The statement above is taken from the most recent of them; the others are arXiv:1609.08053.

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