An arithmetic criterion for graphs being determined by their generalized $A_\alpha$-spectrum

TL;DR

This paper provides an arithmetic criterion involving the $A_eta$-spectrum to determine when a graph is uniquely identified by its spectrum and its complement, extending spectral graph theory with new algebraic conditions.

Contribution

It introduces a simple arithmetic condition for graphs to be determined by their generalized $A_eta$-spectrum when $eta$ is rational, expanding spectral characterization methods.

Findings

A new criterion based on the determinant of a specific matrix for DGA$_eta$S.

The criterion involves the parity and square-free nature of a scaled determinant.

Full rank conditions over finite fields are also part of the criterion.

Abstract

Let $G$ be a graph on $n$ vertices, its adjacency matrix and degree diagonal matrix are denoted by $A(G)$ and $D(G)$, respectively. In 2017, Nikiforov \cite{0007} introduced the matrix $A_{\alpha}(G)=\alpha D(G)+(1-\alpha)A(G)$ for $\alpha\in [0, 1].$ The $A_\alpha$-spectrum of a graph $G$ consists of all the eigenvalues (including the multiplicities) of $A_\alpha(G).$ A graph $G$ is said to be determined by the generalized $A_{\alpha}$-spectrum (or, DGA$_\alpha$S for short) if whenever $H$ is a graph such that $H$ and $G$ share the same $A_{\alpha}$-spectrum and so do their complements, then $H$ is isomorphic to $G$. In this paper, when $\alpha$ is rational, we present a simple arithmetic condition for a graph being DGA$_\alpha$S. More precisely, put $A_{c_\alpha}:={c_\alpha}A_\alpha(G),$ here ${c_\alpha}$ is the smallest positive integer such that $A_{c_\alpha}$ is an integral matrix. Let $\tilde{W}_{{\alpha}}(G)=\left[{\bf 1},\frac{A_{c_\alpha}{\bf 1}}{c_\alpha},\ldots, \frac{A_{c_\alpha}^{n-1}{\bf 1}}{c_\alpha}\right]$, where ${\bf 1}$ denotes the all-ones vector. We prove that if $\frac{\det \tilde{W}_{{\alpha}}(G)}{2^{\lfloor\frac{n}{2}\rfloor}}$ is an odd and square-free integer and the rank of $\tilde{W}_{{\alpha}}(G)$ is full over $\mathbb{F}_p$ for each odd prime divisor $p$ of $c_\alpha$, then $G$ is DGA$_\alpha$S except for even $n$ and odd $c_\alpha\,(\geqslant 3)$. By our obtained results in this paper we may deduce the main results in \cite{0005} and \cite{0002}.