On the location of zeros of the Laplacian matching polynomials of graphs

Abstract

The Laplacian matching polynomial of a graph $G$, denoted by $\mathcal{L}\mathcal{M}(G,x)$, is a new graph polynomial whose all roots are nonnegative real numbers. In this paper, we investigate the location of zeros of the Laplacian matching polynomials. Let $G$ be a connected graph. We show that $0$ is a root of $\mathcal{L}\mathcal{M}(G,x)$ if and only if $G$ is a tree. We prove that the number of distinct positive zeros of $\mathcal{L}\mathcal{M}(G,x)$ is at least equal to the length of the longest path in $G$. It is also established that the zeros of $\mathcal{L}\mathcal{M}(G,x)$ and $\mathcal{L}\mathcal{M}(G-e,x)$ interlace for each edge $e$ of $G$. Using the path-tree of $G$, we present a linear algebraic approach to investigate the largest zero of $\mathcal{L}\mathcal{M}(G,x)$ and particularly to give tight upper and lower bounds on it.