Counting Lattice Points near Kor\'anyi Spheres via Generalized Radon Transforms

TL;DR

This paper develops new bounds for counting lattice points near Korányi spheres in Heisenberg groups by using generalized Radon transforms, overcoming curvature degeneracy and improving previous estimates.

Contribution

It introduces a novel approach employing generalized Radon transforms to bound lattice points near Korányi spheres, considering Heisenberg group structure and non-isotropic dilations.

Findings

Established upper bounds for lattice points near Korányi spheres in Heisenberg groups.

Achieved a logarithmic improvement over previous bounds in lower dimensions.

Extended bounds to more general spheres with Heisenberg homogeneous norms.

Abstract

In this note, we study a lattice point counting problem for spheres in Heisenberg groups, incorporating both the non-isotropic dilation structure and the non-commutative group law. More specifically, we establish an upper bound for the average number of lattice points in a $\delta$-neighborhood of a Kor\'anyi sphere of large radius, where the average considered is over Heisenberg group translations of the sphere. This is in contrast with previous works, which either count lattice points on dilates of a fixed sphere (see \cites{GNT, Gath2}) or consider averages over Euclidean translations of the sphere (see \cites{CT}). We observe that incorporating the Heisenberg group structure allows us to circumvent the degeneracy arising from the vanishing of the Gaussian curvature at the poles of the Kor\'anyi sphere. In fact, in lower dimensions (the first and second Heisenberg group), our method establishes an upper bound for this number which gives a logarithmic improvement over the bound implied by the previously known results. Even for the higher dimensional Heisenberg groups, we recover the bounds implied by the main result of \cite{GNT} using a completely different approach of generalized Radon transforms. Further, we obtain upper bounds for the average number of lattice points near more general spheres described with respect to radial, Heisenberg homogeneous norms as considered in \cite{GNT}.