A quantitative version of the non-abelian idempotent theorem
arXiv:0912.0308 · doi:10.1007/s00039-010-0107-2
Abstract
Suppose that G is a finite group and A is a subset of G such that 1_A has algebra norm at most M. Then 1_A is a plus/minus sum of at most L cosets of subgroups of G, and L can be taken to be triply tower in O(M). This is a quantitative version of the non-abelian idempotent theorem.
82 pp. Changed the title from `Indicator functions in the Fourier-Eymard algebra'. Corrected the proof of Lemma 19.1. Expanded the introduction. Corrected typos