$\mathcal{MID}$ and safe quotients for GRWS

Abstract

Geometrically regular weighted shifts (in short, GRWS) are those with weights $α(N,D)$ given by $α_n (N,D) = \sqrt{\frac{p^n + N}{p^n + D}}$, where $p > 1$ and $(N,D)$ is fixed in the open unit square $ (-1, 1)\times (-1, 1)$. We study here the zone of pairs $ (M,P)$ for which the weight $\frac{α(N,D) }{ α(M,P) }$ gives rise to a moment infinitely divisible ($ \mathcal {MID}$) or a subnormal weighted shift, and deduce immediately the analogous results for product weights $α(N,D) α(M,P)$, instead of quotients. Useful tools introduced for this study are a pair of partial orders on the GRWS.