Approximate Duality Conjecture for finite-field bilinear bias

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For a prime pp, let ω\omega be a ppth root of unity with ω≠1\omega\neq1. For subsets A,B⊆FpnA,B\subseteq\mathbb{F}_p^n, define their bias by

Dω(A,B)=∣Ea∼A, b∼B[ω⟨a,b⟩]∣.D_\omega(A,B)=\left|\mathbb{E}_{a\sim A,\,b\sim B}[\omega^{\langle a,b\rangle}]\right|.

Approximate Duality Conjecture. If Dω(A,B)≥εD_\omega(A,B)\geq\varepsilon for some ε>0\varepsilon>0, then there exist subsets A′⊆AA'\subseteq A and B′⊆BB'\subseteq B such that ⟨a,b⟩\langle a,b\rangle is constant for all a∈A′a\in A' and b∈B′b\in B', and

∣A′∣∣B′∣≥2−O(nlog⁡(1/ε))∣A∣∣B∣.|A'||B'|\geq 2^{-O(\sqrt{n\log(1/\varepsilon)})}|A||B|.

The conjecture was proposed as an approach to the log-rank conjecture and is used in the paper to derive results on set systems with prescribed intersection sizes. The supplied text explicitly says that it remains open, although partial progress is known.

References

Primary source

Zach Hunter, Aleksa Milojević, Benny Sudakov and István Tomon, “Disjoint pairs in set systems and combinatorics of low rank matrices”, arXiv:2411.13510 (2024).

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