Kakeya-type sum-difference constant
Description of constant
$C_{3b} = SD({0,1,\infty};-1)$ is the least exponent such that one has the inequality
\(|A \stackrel{G}{+} B| \leq \max(|A|, |B|, |A \stackrel{G}{-} B|)^{C_{13}}\)
whenever $A, B$ are finite subsets of reals and $G \subset A \times B$, where
\(A \stackrel{G}{\pm} B := \{ a \pm b: a \in A, b \in B\}.\)
Known upper bounds
| Bound |
Reference |
Comments |
| 2 |
Trivial |
|
| $2 - \frac{1}{14} = 1.92857\dots$ |
Wolff (unpublished) |
|
| $2 - \frac{1}{13} = 1.92307\dots$ |
[B1999] |
|
| $2 - \frac{1}{6} = 1.83333\dots$ |
[KT1999] |
|
Known lower bounds
| Bound |
Reference |
Comments |
| $\frac{\log 3}{\log 2} = 1.58496\dots$ |
Trivial |
|
| $\frac{\log 27}{\log (27/4)} = 1.72598\dots$ |
Ruzsa (unpublished) |
|
| $1.77898$ |
[L2015] |
|
| $>1.77898$ |
[GGSWT2025] |
Improved [L2015] in the eighth decimal place (AlphaEvolve) |
- Has many other formulations [GR2019], including an entropy formulation: $C_{3b}$ is the smallest constant such that for any pair of discrete random variables $X,Y$ one has
\(H(X,Y) \leq C_{3b} \max( H(X), H(Y), H(X-Y)).\)
- In [B1999] it was observed that Kakeya sets in dimension $d$ have Minkowski and Hausdorff dimension at least $\frac{d-1}{C_{3b}} + 1$. (This is no longer the best bound in any dimension.)
- Related to the arithmetic Kakeya conjecture [KT2002], [GR2019], which considers other sets of slopes than $0,1,\infty$.
References
- [B1999] Bourgain, J. On the dimension of Kakeya sets and related maximal inequalities. Geom. Funct. Anal. 9 (1999), no. 2, 256-282. DOI: 10.1007/s000390050087.
- [GGSWT2025] Georgiev, Bogdan; Gómez-Serrano, Javier; Tao, Terence; Wagner, Adam Zsolt. Mathematical exploration and discovery at scale. arXiv:2511.02864
- [GR2019] Green, B.; Ruzsa, I. Z. On the arithmetic Kakeya conjecture of Katz and Tao. Periodica Mathematica Hungarica, Volume 78, Issue 1, pp 135–151 (2019). DOI: 10.1007/s10958-018-2003-3.
- [L2015] Lemm, Marius. New counterexamples for sums-differences. Proceedings of the American Mathematical Society, Vol. 143, No. 9 (SEPTEMBER 2015), pp. 3863-3868 (6 pages). DOI: 10.1090/proc/12731.
- [KT1999] Katz, Nets Hawk; Tao, Terence. Bounds on arithmetic projections, and applications to the Kakeya conjecture. Math. Res. Lett. 6 (1999), no. 5-6, 625-630. DOI: 10.4310/MRL.1999.v6.n6.a3.
- [KT2002] Katz, N. H.; Tao, T. New bounds for Kakeya problems. J. Anal. Math. 87 (2002), 231–263. DOI: 10.1007/BF02792310.