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Interlacings for random walks on weighted graphs and the interchange process

We study Aldous' conjecture that the spectral gap of the interchange process on a weighted undirected graph equals the spectral gap of the random walk on this graph. We present a conjecture in the form of an inequality, and prove that this inequality implies Aldous' conjecture by combining an interlacing result for Laplacians of random walks on weighted graphs with representation theory. We prove the conjectured inequality for several important instances. As an application of the developed theory, we prove Aldous' conjecture for a large class of weighted graphs, which includes all wheel graphs, all graphs with four vertices, certain nonplanar graphs, certain graphs with several weighted cycles of arbitrary length, as well as all trees. Caputo, Liggett, and Richthammer have recently resolved Aldous' conjecture, after independently and simultaneously discovering the key ideas developed in the present paper.