The Kővari-Sós-Turán theorem for $\mathrm{GF}(q)$-representable matroids

Abstract

In this paper, we establish an analogue of the Kővari-Sós-Turán Theorem for $\mathrm{GF}(q)$-representable matroids. For $2\le s\le t$, we show that if $M$ is a rank-$n$ simple $\mathrm{GF}(q)$-representable matroid having no $M(K_{s,t})$-restriction, then \[ |E(M)|=O_{q,s,t}\bigl(q^{(1-1/s)n}\bigr). \] In particular, we prove that the maximum number of elements in a simple rank-$n$ binary matroid with no $M(K_{2,t})$-restriction is ${\Theta }_t(2^{n/2})$ where the lower bound is obtained using binary Sidon sets.

11 pages, 1 figure. Note that the use of diacritics in Kővari's name is consistent with the usage in the original paper