Workshop on Graphs and Arithmetic

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There is a long history of interaction between number theory and combinatorics. In the past two decades, deep results in automorphic forms and number theory were used to construct (optimal) expanders, which are known to have wide applications in computer science and communication networks. These techniques were generalized to construct higher dimensional analogues. Very recently, zeta functions for graphs have been extended to complexes. They contain topological and spectral information of the combinatorial objects so that the Riemann hypothesis is satisfied if and only if the object is spectrally extremal. Furthermore, exciting developments in arithmetic combinatorics in recent years provide new tools to construct families of good expanders, which in turn are used to obtain deep number theoretic results. At the same time, the concept of expansion is extended in group theory and computer science to a different new context.A workshop on graphs and arithmetic will take place March 8-12, 2010, at CRM,Montreal, Canada, to review recent exciting developments in expanders and number theory. The focus will be on the interconnections between combinatorics, group theory and number theory. Both theories and applications will be emphasized. Seventeen invited speakers are from the US. To cover the expenses of the invited speakers and partially support graduate students and recent doctorates, support from the NSF is sought to supplement the fundscommitted by the CRM.