Existence results for Kazdan-Warner type equations on graphs

Abstract: In this paper, motivated by the work of Huang-Lin-Yau (Commun. Math. Phys. 2020), Sun-Wang (Adv. Math. 2022) and Li-Sun-Yang (Calc. Var. Partial Differential Equations 2024), we investigate the existence of Kazdan-Warner type equations on a finite connected graph, based on the theory of Brouwer degree. Specifically, we consider the equation \begin{equation*} -\Delta u=h(x)f(u)-c, \end{equation*} where $h$ is a real-valued function defined on the vertex set $V$, $c\in\mathbb{R}$ and \begin{equation*} f(u)= \left(1-\displaystyle\frac{1}{1+u^{2n}}\right)e^u \end{equation*} with $n\in \mathbb{N}^*$. Different from the previous studies, the main difficulty in this paper is to show that the corresponding equation has only three constant solutions, based on delicate analysis and the connectivity of graphs, which have not been extensively explored in previous literature.