English

Packing dimension of vertical projections in the Heisenberg group

Classical Analysis and ODEs 2026-03-10 v10 Metric Geometry

Abstract

It is shown that if AA is a Borel subset of the first Heisenberg group, with Hausdorff dimension satisfying 2<dimA<32< \dim A < 3, then the packing dimensions of vertical projections of AA are almost surely not less than dimA\dim A, where both packing and Hausdorff dimensions are defined with respect to the Kor\'anyi metric. For the Hausdorff dimension of the projections, a weaker almost sure lower bound is obtained which improves the known bound in the range 2<dimA<18(17+33)2.842 < \dim A < \frac{1}{8}\left( 17 + \sqrt{33}\right) \approx 2.84. The bound is slightly larger than 1+12dimA1+\frac{1}{2} \dim A and behaves similarly near dimA=2\dim A =2. Both proofs rely on a variable coefficient local smoothing inequality.

Keywords

Cite

@article{arxiv.2407.11475,
  title  = {Packing dimension of vertical projections in the Heisenberg group},
  author = {Terence L. J. Harris},
  journal= {arXiv preprint arXiv:2407.11475},
  year   = {2026}
}

Comments

34 pages. V8: Proof fixed by using packing instead of Hausdorff dimension. V10: Added partial result for Hausdorff dimension which restores result from V4 with small improvement