On the Aα-spectra of trees.

Let G be a graph with adjacency matrix A ( G ) and let D ( G ) be the diagonal matrix of the degrees of G . For every real α ∈ [ 0 , 1 ] , define the matrix A α ( G ) as A α ( G ) = α D ( G ) + ( 1 − α ) A ( G ) . This paper gives several results about the A α -matrices of trees. In particular, it is shown that if T Δ is a tree of maximal degree Δ, then the spectral radius of A α ( T Δ ) satisfies the tight inequality ρ ( A α ( T Δ ) ) < α Δ + 2 ( 1 − α ) Δ − 1 , which implies previous bounds of Godsil, Lovász, and Stevanović. The proof is deduced from some new results about the A α -matrices of Bethe trees and generalized Bethe trees. In addition, several bounds on the spectral radius of A α of general graphs are proved, implying tight bounds for paths and Bethe trees. [ABSTRACT FROM AUTHOR]