On the distribution of Sidon series

Abstract

Let B denote an arbitrary Banach space, G a compact abelian group with Haar measure $μ$ and dual group $Γ$. Let E be a Sidon subset of $Γ$ with Sidon constant S(E). Let r_n denote the n-th Rademacher function on [0, 1]. We show that there is a constant c, depending only on S(E), such that, for all $α> 0$: c^{-1}P[| \sum_{n=1}^Na_nr_n| >= c α] <= μ[| \sum_{n=1}^Na_nγ_n| >= α] <= cP [|\sum_{n=1}^Na_nr_n| >= c^{-1} α]