The Dirichlet-Bohr radius

Abstract

Denote by Ω(n) the number of prime divisors of n ∈ ℕ (counted with multiplicities). For x ∈ ℕ define the Dirichlet-Bohr radius L(x) to be the best r > 0 such that for every finite Dirichlet polynomial Σn≤xann-s we have ∑n ≤ x |an| rΩ(n) ≤ supt ∈ ℝ | ∑n ≤ x ann-it|. We prove that the asymptotically correct order of L(x) is (log x)1/4x-1/8. Following Bohr's vision our proof links the estimation of L(x) with classical Bohr radii for holomorphic functions in several variables. Moreover, we suggest a general setting which allows translating various results on Bohr radii in a systematic way into results on Dirichlet-Bohr radii, and vice versa.