Documents  Perret, Marc | enregistrements trouvés : 3

Research talks;Algebraic and Complex Geometry;Number Theory

A $d$-regular graph is Ramanujan if its nontrivial eigenvalues in absolute value are bounded by $2\sqrt{d-1}$. By means of number-theoretic methods,infinite families of Ramanujan graphs were constructed by Margulis and independently by Lubotzky-Phillips-Sarnak in 1980's for $d=q+ 1$, where q is a prime power. The existence of an infinite family of Ramanujan graphs for arbitrary d has been an open question since then. Recently Adam Marcus, Daniel Spielman and Nikhil Srivastava gave a positive answer to this question by showing that any bipartite $d$-regular Ramanujan graph has a $2$-fold cover that is also Ramanujan. In this talk we shall discuss their approach and mentionsimilarities with function field towers. A $d$-regular graph is Ramanujan if its nontrivial eigenvalues in absolute value are bounded by $2\sqrt{d-1}$. By means of number-theoretic methods,infinite families of Ramanujan graphs were constructed by Margulis and independently by Lubotzky-Phillips-Sarnak in 1980's for $d=q+ 1$, where q is a prime power. The existence of an infinite family of Ramanujan graphs for arbitrary d has been an open question since then. Recently Adam Marcus, Daniel ...

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- 51 p.

Localisation : Ouvrage RdC (PERR)

Courbes algébriques sur un corps fini # borne de Weil # tours de corps de classes # fonctions L # Sommes de caractères # codes correcteurs d'erreurs # borne de Varshamov-Gilbert # empilements de sphères

14H25 ; 14G15 ; 94B27 ; 14G05 ; 14N10

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