Tao's asymptotic tightness conjecture for colored product-free subsets

Let GG be a finite group, let F\mathbb{F} be a field, and let X1,,XkX_1,\dots,X_k be subspaces of the group algebra F[G]\mathbb{F}[G] satisfying

X1Xk=0.X_1\cdots X_k=0.

Define Mk(G)M_k(G) to be the minimum, over all choices of the field and all such kk-tuples of subspaces, of

i=1kcodimXi.\sum_{i=1}^k \operatorname{codim} X_i.

A kk-colored product-free subset of GG is a set of kk-tuples with no product relation of the relevant colored form. Tao's asymptotic tightness conjecture. For sufficiently large G|G|, the maximal cardinality of a kk-colored product-free subset of GG is

Mk(G)Go(1).M_k(G)\cdot |G|^{o(1)}.

The preceding theorem gives the upper bound by the sum of codimensions, while the conjecture asserts that this bound is asymptotically sharp up to a subpolynomial factor. Tightness is known in logarithmic scale for tri-colored sum-free subsets of Fpn\mathbb{F}_p^n, from work of Kleinberg, Sawin, Speyer, Norin, and Pebody; the corresponding assertion for other groups is posed as an open problem.

Sources & referencesView supporting material

Primary source

Fedor Petrov, “Combinatorial results implied by many zero divisors in a group ring”, arXiv:1606.03256 (2020).

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