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Density spectrum of Cantor measure. (English) Zbl 1523.28004

Summary: Given \(\rho\in(0,1/3]\), let \(\mu\) be the Cantor measure satisfying \(\mu=\frac{1}{2}\mu f^{-1}_0+\frac{1}{2}\mu f^{-1}_1\), where \(f_i(x)=\rho x+i(1-\rho)\) for \(i=0,1\). The support of \(\mu\) is a Cantor set \(C\) generated by the iterated function system \(\{f_0, f_1\}\). Continuing the work of Feng et al (2000) on the pointwise lower and upper densities \[ \Theta^s_*(\mu,x)=\liminf\limits_{r\to 0}\frac{\mu(B(x,r))}{(2r)^s},\quad \Theta^{*s}(\mu,x)=\limsup\limits_{r\to 0}\frac{\mu(B(x,r))}{(2r)^s}, \] where \(s=-\log 2/\log \rho\) is the Hausdorff dimension of \(C\), we give a complete description of the sets \(D_*\) and \(D^*\) consisting of all possible values of the lower and upper densities, respectively. We show that both sets contain infinitely many isolated and infinitely many accumulation points, and they have the same Hausdorff dimension as the Cantor set \(C\). Furthermore, we compute the Hausdorff dimension of the level sets of the lower and upper densities. Our method consists in formulating an equivalent ‘dyadic’ version of the problem involving the doubling map on \([0,1)\), which we solve by using known results on the entropy of a certain open dynamical system and the notion of tuning.

MSC:

28A80 Fractals
26A30 Singular functions, Cantor functions, functions with other special properties
28A78 Hausdorff and packing measures
37B10 Symbolic dynamics

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