Strongly dense free subgroups of semisimple algebraic groups

By Emmanuel Breuillard, Ben Joseph Green, Robert M. Guralnick, Terence Tao. Israel Journal of Mathematics, 2010

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We show that (with one possible exception) there exist strongly dense free subgroups in any semisimple algebraic group over a large enough field. These are nonabelian free subgroups all of whose subgroups are either cyclic or Zariski dense. As a consequence, we get new generating results for finite simple groups of Lie type and a strengthening of a theorem of Borel related to the Hausdorff-Banach-Tarski paradox. In a sequel to this paper, we use this result to also establish uniform expansion properties for random Cayley graphs over finite simple groups of Lie type

Subfields: Discrete Mathematics and Combinatorics, Geometry and Topology

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