On the location of roots of the independence polynomial of bounded degree graphs

Understand

In [1] Peters and Regts confirmed a conjecture by Sokal by showing that for every $\Delta \in \mathbb{Z}_{\geq 3}$ there exists a complex neighborhood of the interval $\left[0, \frac{\left(\Delta - 1\right)^{\Delta - 1}}{\left(\Delta-2\right)^\Delta}\right)$ on which the independence polynomial is nonzero for all graphs of maximum degree $\Delta$.

• Furthermore, they gave an explicit neighborhood $U_\Delta$ containing this interval on which the independence polynomial is nonzero for all finite rooted Cayley trees with branching number $\Delta$.
• The question remained whether $U_\Delta$ would be zero-free for the independence polynomial of all graphs of maximum degree $\Delta$.
• In this paper it is shown that this is not the case.