Nilpotent obstruction conjecture for small tripling in linear groups

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Let KK be a field, and let AA be a finite subset of GL⁡n(K)\operatorname{GL}_n(K) satisfying A=A−1A=A^{-1} and e∈Ae\in A. For every R≥1R\geq 1, consider the alternatives involving the tripling set A3A^3. Nilpotent obstruction conjecture. Either

∣A3∣≥R∣A∣,|A^3|\geq R|A|,

or there exist subgroups H1≤H2H_1\leq H_2 of GL⁡n(K)\operatorname{GL}_n(K) and an integer k=On(1)k=O_n(1) such that H1H_1 and H2H_2 are both normal in ⟨A⟩\langle A\rangle, H2/H1H_2/H_1 is nilpotent, AkA^k contains H1H_1, and

∣Ak∩H2∣≥R−On(1)∣A∣.|A^k\cap H_2|\geq R^{-O_n(1)}|A|.

This is posed as a broad question about describing subsets that fail to grow: failure of substantial tripling should be explained by concentration near a subgroup extension with nilpotent quotient. The supplied text gives no evidence that the proposed statement has been proved or disproved.

References

Primary source

H. A. Helfgott, “Growth in groups: ideas and perspectives”, arXiv:1303.0239 (2015).

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