On the deterministic property for characteristic functions of several variables

Abstract

Assume that $f$ is the characteristic function of a probability measure $\mu_f$ on $R^n$. Let $\sigma>0$. We study the following extrapolation problem: under what conditions on the neighborhood of infinity $V_{\sigma}=\{x\in R^n: |x_k|>\sigma, \ k=1,\dots, n\}$ in $R^n$ does there exist a characteristic function $g$ on $R^n$ such that $g=f$ on $V_{\sigma}$, but $g\not\equiv f$? Let $\mu_f$ have a nonzero absolutely continuous part with continuous density $\varphi$. In this paper certain sufficient conditions on $\varphi$ and $V_{\sigma}$ are given under which the latter question has an affirmative answer. We also address the optimality of these conditions. Our results indicate that not only does the size of both $V_{\sigma}$ and the support ${{\text{\,supp}}\,}\varphi$ matter, but also certain arithmetic properties of ${{\text{\,supp}}\,}\varphi$.