[Combprob] Thursday, Dec 10, Doron Puder on "Ramanujan Coverings of Graphs"

[Daniel Spielman]

In LOM 215 at 4:00.

Dec 10: Doron Puder (IAS): "Ramanujan Coverings of Graphs"

Ramanujan graphs are optimal expander graphs, and their existence and
construction have been the focus of much research during the last three
decades. We prove that every bipartite Ramanujan graph has a d-covering
(a.k.a. d-lift) which is also Ramanujan. This generalizes the d=2 case, a
recent major breakthrough in the subject due to Marcus, Spielman and
Srivastava. The main tools we use are the Peter-Weyl theory in group
representations, as well as the theory of interlacing polynomials.

All notions will be explained. Joint work with Chris Hall and Will Sawin.
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