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On a spectral concentration in Brouwer-type conjecture for a uniform caterpillar graphs
AIMS Mathematics 2026, 11(5): 15199-15214
Published: 15 May 2026
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In this paper, we investigate spectral properties of the distance Laplacian matrix of certain graphs. We derive bounds on the distance Laplacian eigenvalues of a uniform caterpillar graphs and establish Brouwer-type inequalities for a graph with sufficiently large diameter. We verify the Brouwer-type conjecture proposed by Zhou et al. for the class of uniform caterpillar graphs with diameter at least six, thereby confirming its validity for a new infinite family of trees. The inequality U r ( G ) W ( G ) + ( r + 2 3 ) holds for all 1 r n 1 , where U r ( G ) is the sum of the r largest distance Laplacian eigenvalues, and W ( G ) is the Wiener index. Moreover, we show that the normalized spectral sums U r ( G ) / r λ 1 ( G ) form a strictly decreasing sequence for small values of r and converge to a constant strictly less than one as r n 1, revealing a spectral compression phenomenon in the distance Laplacian spectrum. Several analytical bounds are provided to demonstrate the tightness of the obtained results.

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