On the $A_\alpha$-spectral radius of graphs without linear forests

Abstract

Let $A(G)$ and $D(G)$ be the adjacency and degree matrices of a simple graph $G$ on $n$ vertices, respectively. The \emph{$A_\alpha$-spectral radius} of $G$ is the largest eigenvalue of $A_\alpha (G)=\alpha D(G)+(1-\alpha)A(G)$ for a real number $\alpha \in[0,1]$. In this paper, for $\alpha \in (0,1)$, we obtain a sharp upper bound for the $A_\alpha$-spectral radius of graphs on $n$ vertices without a subgraph isomorphic to a liner forest for $n$ large enough and characterize all graphs which attain the upper bound. As a result, we completely obtain the maximum signless Laplacian spectral radius of graphs on $n$ vertices without a subgraph isomorphic to a liner forest for $n$ large enough.