arXiv:2003.13829v2
Abstract
Let be a bounded convex domain in symmetric about the origin. The critical locus of is defined to be the (non-empty compact) set of lattices in of smallest possible covolume such that . These are classical objects in geometry of numbers; yet all previously known examples of critical loci were either finite sets or finite unions of closed curves. In this paper we give a new construction which, in particular, furnishes examples of domains having critical locus of arbitrary Hausdorff dimension between and .
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01Statements2 reported findingsCorrect
Every nonempty closed subset of the critical circle of a strictly convex irreducible planar domain is correctly realized as the full critical locus of a larger symmetric convex domain. The disc and arbitrary-dimension consequences follow.
Closed subsets of an irreducible critical circle are realizable
Pages 3 and 7--8 · main theorem and its proof · arXiv:2003.13829v2
The critical lattices of the irreducible domain are continuously parameterized by one boundary contact point and the next contact point. For each complementary interval of the prescribed closed parameter set, adjoining the tangent-bounded curvilinear region moves exactly that open boundary arc into the interior. Lattices with parameters in the closed set retain the three boundary contacts and remain admissible; every excluded parameter acquires an interior lattice point. The critical determinant comparison then identifies the critical locus exactly.
Arbitrary closed subsets and Hausdorff dimensions occur
Pages 2--3 · unit-disc specialization · arXiv:2003.13829v2
The unit disc is strictly convex and irreducible, and its critical locus is the rotation circle of the hexagonal lattice. Applying the realization theorem to any nonempty closed subset of that circle gives the stated domain. Choosing a closed subset of any prescribed Hausdorff dimension in yields every dimension between and .
02Proofs3 reported findingsCorrect
The critical-locus parametrization, tangent-region construction, and determinant comparison are correct. A repeated inequality in the comparison lemma has a unique typographical correction.
Mahler's contact-point lemmas give a genuine homeomorphism
Pages 5--6 · proof of the critical-locus parametrization theorem · arXiv:2003.13829v2
Uniqueness of the critical lattice through each boundary point makes the parametrization well-defined. The interlacing lemma forces continuity of the next contact point, and compactness plus injectivity turns the descended circle map into a homeomorphism. The parallelogram exception is excluded exactly where the six-contact argument would fail.
The first critical-determinant inequality repeats the wrong symbol
Page 6 · proof of Lemma 3.1 · arXiv:2003.13829v2
The proof prints after assuming . Admissibility gives . The next sentence uses a lattice that is both -critical and -admissible to prove the reverse inequality, so replacing the second by is uniquely determined and restores the displayed equality used below.
The admissible-lattice characterization is applied in both directions
Pages 7--8 · proof of the main realization theorem · arXiv:2003.13829v2
At retained parameters, the three vectors , , and remain on the new boundary, so the contact-point criterion gives admissibility. At an omitted parameter, lies in the added interior region, so the corresponding lattice is not admissible. Since one retained lattice is admissible, the corrected comparison lemma gives equality of critical determinants and completes the exact-locus argument.
03Novelty0 reported findingsNo non-novelty findings
No non-novelty findings.