Bar-Ilan Combinatorics Seminar (joint with the Department of Mathematics Colloquium) (when) Sunday, 12 Tevet (Dec. 19), 12:00-13:00 *** NOTE SPECIAL TIME *** (where) Room 201 (Math Department Seminar Room), Math and CS Building (216), Bar-Ilan University (who) Benny Sudakov (UCLA) (what) "Expanders, Ramanujan graphs and random lifts" Abstract: Expansion of a graph is one of the most fundamental concepts in modern combinatorics, which has numerous applications in many mathematical areas. It is well known that expansion is closely relates to the spectral properties of the graph. The celebrated Alon-Boppana bound says that all eigenvalues of a d-regular graph must be at least 2sqrt(d-1) - o(1), and graphs that meet this bound are called Ramanujan Graphs. There are still many unresolved questions about the existence of such graphs. In this talk we survey this background material, and then explain what lifts of graphs are and how the above questions can be approached using random lifts of graphs. Joint work with Lubetzky and Vu. ************************************************************************* You are all invited! (Graduate students especially welcome) Seminar organizer: Ron Adin <radin@math.biu.ac.il> Seminar's homepage: <http://www.math.biu.ac.il/~radin/comsem/comsem.html> ************************************************************************* --------------------------------------------------------- Technion Math Net-2 (TECHMATH2) Editor: Michael Cwikel <techm@math.technion.ac.il> Announcement from: Ron Adin <radin@math.biu.ac.il>