English

On off-diagonal Ramsey numbers for vector spaces over $\mathbb{F}_{2}$

Combinatorics 2024-12-24 v2 Number Theory

Abstract

For every positive integer dd, we show that there must exist an absolute constant c>0c > 0 such that the following holds: for any integer ncd7n \geq cd^{7} and any red-blue coloring of the one-dimensional subspaces of F2n\mathbb{F}_{2}^{n}, there must exist either a dd-dimensional subspace for which all of its one-dimensional subspaces get colored red or a 22-dimensional subspace for which all of its one-dimensional subspaces get colored blue. This answers recent questions of Nelson and Nomoto, and confirms that for any even plane binary matroid NN, the class of NN-free, claw-free binary matroids is polynomially χ\chi-bounded. Our argument will proceed via a reduction to a well-studied additive combinatorics problem, originally posed by Green: given a set AF2nA \subset \mathbb{F}_{2}^{n} with density α[0,1]\alpha \in [0,1], what is the largest subspace that we can find in A+AA+A? Our main contribution to the story is a new result for this problem in the regime where 1/α1/\alpha is large with respect to nn, which utilizes ideas from the recent breakthrough paper of Kelley and Meka on sets of integers without three-term arithmetic progressions.

Keywords

Cite

@article{arxiv.2309.02424,
  title  = {On off-diagonal Ramsey numbers for vector spaces over $\mathbb{F}_{2}$},
  author = {Zach Hunter and Cosmin Pohoata},
  journal= {arXiv preprint arXiv:2309.02424},
  year   = {2024}
}

Comments

incorporated referee comments; to appear in Math. Proc. Camb. Phil. Soc

R2 v1 2026-06-28T12:13:25.829Z