A New Bound on Partial Sum-sets and Difference-sets, and Applications to the Kakeya Conjecture

Let A, B, be finite subsets of an abelian group, and let G ⊂ A×B be such that #A,#B,#{a + b : (a, b) ∈ G} ≤ N . We consider the question of estimating the quantity #{a − b : (a, b) ∈ G}. In [2] Bourgain improved the trivial upper bound of N to N 1 13 , and applied this to the Kakeya conjecture. We improve Bourgain’s estimate further to N 1 6 , and conclude that Besicovitch sets in Rn have Hausdorff and Minkowski dimension at least 6n 11 + 5 11 . This is new for n > 12.