Joint Complete Monotonicity of reciprocal of a polynomial in two variables

Abstract: In this article, we study the problem of classifying polynomials $p:\mathbb{R}^2_+\to (0,\infty)$ for which the net ${\frac{1}{p(m,n)}}{m,n\in \mathbb{Z}+}$ is joint completely monotone, where $p(x,y)=b(x)+a(x)y$, $a(x)$ and $b(x)$ are polynomials with $deg(a) < deg(b)$. We prove a sufficient condition when $deg(a) = deg(b)-1$ and obtain a necessary condition when $deg(a) < deg(b)$. In the case when $deg(b)=3$ and $deg(a)=1$, we give a family of possible values of the roots of $a(x)$ and $b(x)$ such that the net ${\frac{1}{p(m,n)}}{m,n\in \mathbb{Z}+}$ is not joint completely monotone. Further, in some cases where a sufficient condition is satisfied by the net ${\frac{1}{p(m,n)}}{m,n\in \mathbb{Z}+}$, we obtain the corresponding reproducing kernel Hilbert space and a subnormal weighted shift on it. We study some properties of this weighted shift.