Spectrality and eigen sets of infinite convolutions and random measures generated by admissible pairs
In this paper, we construct a class of random measures $μ^{\mathbf{n}}$ by infinite convolutions. Given admissible pairs $\{(N_{k}, B_{k})\}_{k=1}^{m}$ and a sequence $\bn=\{n_{k}\}_{k=1}^{\infty}$ of positive integers, for every $\bw\in Ω$, we write $μ^{\mathbf{n}}(\bw) = δ_{N_{ω_{1}}^{-n_{1}}B_{ω_{1}}} * δ_{N_{ω_{1}}^{-n_{1}}N_{ω_{2}}^{-n_{2}}B_{ω_{2}}} * \cdots$. First, we show that the mapping $μ^{\mathbf{n}}: (\bw, B) \mapsto μ^{\mathbf{n}}(\bw)(B)$ is a random measure. Next, we introduce the notion of a $t$-equi-positive family, and use it to obtain a general sufficient condition under which an infinite convolution is a spectral measure and possesses a specified set of spectral eigenvalues. We then extend the concepts of spectrality and spectral eigenvalues to random measures, and show that, under the assumption that the corresponding standard infinite convolution is non-degenerate for $\mathbb{P}$-a.e.\ $\boldsymbolω\inΩ$, the measures $μ^{\mathbf{n}}$ are spectral random measures for $\mathbb{P}$-a.e.\ $\boldsymbolω$, admitting the spectral eigen set \[ \mathcal{E}_m=\{t\in\mathbb{N}_+:\gcd(t,N_k)=1,\,1\le k\le m\}. \] Moreover, for each such $t$, there exist uncountably many spectra $Λ_{\boldsymbolω}\subset\mathbb{Z}$ with $tΛ_{\boldsymbolω}$ also a spectrum of $μ^{\mathbf{n}}(\boldsymbolω)$. Finally, for the important case where each digit set $B_k$ is a consecutive set $\{0,1,\dots,b_k-1\}$, we completely characterise the positive integer spectral eigenvalues of $μ^{\mathbf{n}}(\boldsymbolω)$, proving that they are exactly the integers coprime to every $b_k$.