Sufficient conditions for the variation of toughness under the distance spectral in graphs involving minimum degree

Abstract

The concept of graph toughness was first introduced in 1973. In 1995, scholars first explored the lower bound of the toughness of connected d-regular graphs with respect to d and the second largest eigenvalue of the adjacency matrix. The concept of the variation of toughness was first introduced in 1988. The variation of toughness is defined as tau(G) = min{|S|/(c(G-S)-1)}. In 2025, Chen, Fan, and Lin provided sufficient conditions for a graph to be t-tough in terms of the minimum degree and the distance spectral radius. Inspired by this, we propose a sufficient condition for a graph to be tau-tough in terms of minimum degree and distance spectral radius, and provide the corresponding proof, where |S| and c(G-S)-1 are mutually divisible.