Sharp refined-direction Kakeya estimates in finite Heisenberg groups

Abstract: Let $n\geq 2$ and let $q$ be an odd prime power. The first aim of this paper is to prove that, for every $E\subset \mathbb{H}<em>n(\mathbb{F}_q)$ and every $λ&gt;0$, the following sharp rich-direction estimate holds [ \left| \left{ \vartheta\in D_n: M^{\mathrm{rd}}{\mathbb{H}_n}\mathbf{1}_E(\vartheta)\geqλ \right} \right| \lesssim_n q^{2n-1}|E|λ^{-2n}. ] The second aim is to determine, for every $1\leq u,v\leq\infty$, the sharp exponent of $q$ in the corresponding $\ell<sup>u\to\ell<sup>v$ estimate. More precisely, we prove that [ A_n^{\mathrm{rd}}(u,v) = \max\left{ \frac{2n-1}{v},\ 1-\frac1u,\ \frac{2n}{v}-\frac1u,\ 1+\frac{2n}{v}-\frac{2n+1}{u} \right}. ] The proof combines the polynomial method with multiplicities and a probabilistic covering argument based on the action of the affine symplectic group.