Abstract

In this note we present an algorithm to obtain a uniform lower bound on Hausdorff dimension of the stationary measure of an affine iterated function scheme with similarities, the best known example of which is Bernoulli convolution. The Bernoulli convolution measure μλ is the probability measure corresponding to the law of the random variableξ=∑k=0∞ξkλk, where ξk are i.i.d. random variables assuming values −1 and 1 with equal probability and 12<λ<1. In particular, for Bernoulli convolutions we give a uniform lower bound dimH⁡(μλ)≥0.96399 for all 12<λ<1.

Highlights

  • The study of the properties of Bernoulli convolutions was greatly advanced by two influential papers of Paul Erdos from 1939 [5] and 1940 [6] and has remained an active area of research ever since

  • Ξ = ξkλk k=0 where∞ k=1 are independent random variables assuming values ±1 with equal probability

  • We introduce two alternative characteristics of dimension type, namely, the correlation dimension and the Frostman dimension, which are easier to estimate and give a lower bound on the Hausdorff dimension

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Summary

INTRODUCTION

The study of the properties of Bernoulli convolutions was greatly advanced by two influential papers of Paul Erdos from 1939 [5] and 1940 [6] and has remained an active area of research ever since. Any measure μ which is absolutely continuous with respect to Lebesgue measure automatically satisfies dimH(μ) = 1, and the result of Shmerkin implies that dimH(μλ) = 1 for all but an exceptional set of parameters λ of zero Hausdorff dimension. Lower bounds on the dimensions of the Bernoulli convolutions for the reciprocals of small Salem numbers are presented in Appendix A.2 Another conjecture suggests that there exists ε > 0 such that for any λ ∈ (1 − ε, 1) the dimension of the measure μλ equals 1. The Lehmer’s conjecture states that the Mahler measure of any nonzero noncyclotomic irreducible polynomial with integer coefficients is bounded below by some constant c > 1 It implies, in particular, that there exists a smallest Salem number.

Iterated function schemes with similarities
Approach to lower bounds for Hausdorff dimension
Affine iterated function schemes with similarities
General uniformly contracting schemes
Approach to lower bounds for Hausdorff dimension ψ
DIMENSION OF A MEASURE
Dimension of a measure
Hausdorff dimension
Correlation dimension
Frostman dimension
COMPUTING LOWER BOUNDS
Extension to open set of parameters
Constructing the test function
Verifying a conjectured value
Computing a lower bound
Selected algebraic parameter values
Estimates for Salem numbers
Random processes viewpoint
Effectiveness of the algorithm
A Numerical data
Full Text
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