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Approximate Subgroups of Linear Groups

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Abstract

We establish various results on the structure of approximate subgroups in linear groups such as SL n (k) that were previously announced by the authors. For example, generalising a result of Helfgott (who handled the cases n = 2 and 3), we show that any approximate subgroup of \({{\rm SL}_{n}({\mathbb {F}}_{q})}\) which generates the group must be either very small or else nearly all of \({{\rm SL}_{n}({\mathbb {F}}_{q})}\). The argument generalises to other absolutely almost simple connected (and non-commutative) algebraic groups G over an arbitrary field k and yields a classification of approximate subgroups of G(k). In a subsequent paper, we will give applications of this result to the expansion properties of Cayley graphs.

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Breuillard, E., Green, B. & Tao, T. Approximate Subgroups of Linear Groups. Geom. Funct. Anal. 21, 774–819 (2011). https://doi.org/10.1007/s00039-011-0122-y

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