On the Skitovich-Darmois theorem for a-adic solenoids

TL;DR

This paper extends the Skitovich-Darmois theorem to a-adic solenoids, showing that for three linear forms of three independent variables, independence implies at least one distribution is idempotent, unlike the classical case.

Contribution

It proves a new version of the Skitovich-Darmois theorem for a-adic solenoids involving three variables, where previously the theorem failed for two variables.

Findings

Independence of three linear forms implies at least one distribution is idempotent.

The classical Skitovich-Darmois theorem does not hold for two variables on these groups.

Characterization of all a-adic solenoids where this property holds.

Abstract

Let $X$ be a compact connected Abelian group. It is well-known that then there exist topological automorphisms $\alpha_j, \beta_j $ of $X$ and independent random variables $\xi_1$ and $\xi_2$ with values in $X$ and distributions $\mu_1, \mu_2$ such that the linear forms $L_1 = \alpha_1\xi_1 + \alpha_2\xi_2$ and $L_2 = \beta_1\xi_1 + \beta_2\xi_2$ are independent, whereas $\mu_1$ and $\mu_2$ are not represented as convolutions of Gaussian and idempotent distributions. This means that the Skitovich--Darmois theorem fails for such groups. We prove that if we consider three linear forms of three independent random variables taking values in $X$, where $X$ is an ${\boldsymbol a}$-adic solenoid, then the independence of the linear forms implies that at least one of the distributions is idempotent. We describe all such solenoids.