English

$\delta$-Badly approximable numbers and ubiquitously losing sets

Number Theory 2026-05-15 v2 Dynamical Systems

Abstract

We consider a natural filtration Bad(δ)Bad(δ)\boldsymbol{\operatorname{Bad}}(\delta) \subset \boldsymbol{\operatorname{Bad}}(\delta') for δδ>0\delta \geq \delta'>0 on the set of badly approximable numbers to complement the filtration of the well approximable numbers by the τ\tau-well approximable numbers. We show that the set Bad(δ)\boldsymbol{\operatorname{Bad}}(\delta) is a (1/3,18δ)(1/3, 18 \delta)-winning set and give a lower bound on its Hausdorff dimension. We introduce the notion of (α,β)(\alpha, \beta)-ubiquitously losing sets\textit{ubiquitously losing sets} to the theory of Schmidt games, give an upper bound on the Hausdorff dimension of an (α,β)(\alpha, \beta)-ubiquitously losing set that is strictly less than full Hausdorff dimension, show that Bad(δ)\boldsymbol{\operatorname{Bad}}(\delta) is a (1/2,18/δ)(1/2, 18/\delta)-ubiquitously losing set, and give an upper bound on the Hausdorff dimension of Bad(δ)\boldsymbol{\operatorname{Bad}}(\delta) that is strictly less than one. Combined with a finite intersection property and a bilipschitz transfer property, we obtain results for finite intersections of translates of Bad(δ)\boldsymbol{\operatorname{Bad}}(\delta).

Keywords

Cite

@article{arxiv.2605.06325,
  title  = {$\delta$-Badly approximable numbers and ubiquitously losing sets},
  author = {Jimmy Tseng},
  journal= {arXiv preprint arXiv:2605.06325},
  year   = {2026}
}

Comments

77 pages. Introduction revised

R2 v1 2026-07-01T12:55:10.891Z