MathematikaPub Date : 2023-08-14DOI: 10.1112/mtk.12221
Dmitry Kleinbock, Anurag Rao
{"title":"A dichotomy phenomenon for bad minus normed Dirichlet","authors":"Dmitry Kleinbock, Anurag Rao","doi":"10.1112/mtk.12221","DOIUrl":"10.1112/mtk.12221","url":null,"abstract":"<p>Given a norm ν on <math>\u0000 <semantics>\u0000 <msup>\u0000 <mi>R</mi>\u0000 <mn>2</mn>\u0000 </msup>\u0000 <annotation>$mathbb {R}^2$</annotation>\u0000 </semantics></math>, the set of ν-Dirichlet improvable numbers <math>\u0000 <semantics>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 <annotation>$mathbf {DI}_nu$</annotation>\u0000 </semantics></math> was defined and studied in the papers (Andersen and Duke, <i>Acta Arith</i>. 198 (2021) 37–75 and Kleinbock and Rao, <i>Internat. Math. Res. Notices</i> 2022 (2022) 5617–5657). When ν is the supremum norm, <math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 <mo>=</mo>\u0000 <mi>BA</mi>\u0000 <mo>∪</mo>\u0000 <mi>Q</mi>\u0000 </mrow>\u0000 <annotation>$mathbf {DI}_nu = mathbf {BA}cup {mathbb {Q}}$</annotation>\u0000 </semantics></math>, where <math>\u0000 <semantics>\u0000 <mi>BA</mi>\u0000 <annotation>$mathbf {BA}$</annotation>\u0000 </semantics></math> is the set of badly approximable numbers. Each of the sets <math>\u0000 <semantics>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 <annotation>$mathbf {DI}_nu$</annotation>\u0000 </semantics></math>, like <math>\u0000 <semantics>\u0000 <mi>BA</mi>\u0000 <annotation>$mathbf {BA}$</annotation>\u0000 </semantics></math>, is of measure zero and satisfies the winning property of Schmidt. Hence for every norm ν, <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>BA</mi>\u0000 <mo>∩</mo>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation>$mathbf {BA} cap mathbf {DI}_nu$</annotation>\u0000 </semantics></math> is winning and thus has full Hausdorff dimension. In this article, we prove the following dichotomy phenomenon: either <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>BA</mi>\u0000 <mo>⊂</mo>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation>$mathbf {BA} subset mathbf {DI}_nu$</annotation>\u0000 </semantics></math> or else <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>BA</mi>\u0000 <mo>∖</mo>\u0000 <msub>\u0000 <mi>DI</mi>\u0000 <mi>ν</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation>$mathbf {BA} setminus mathbf {DI}_nu$</annotation>\u0000 ","PeriodicalId":18463,"journal":{"name":"Mathematika","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46726104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
MathematikaPub Date : 2023-08-13DOI: 10.1112/mtk.12218
Angelica Babei, Andrew Fiori, Cameron Franc
{"title":"Families of ϕ-congruence subgroups of the modular group","authors":"Angelica Babei, Andrew Fiori, Cameron Franc","doi":"10.1112/mtk.12218","DOIUrl":"10.1112/mtk.12218","url":null,"abstract":"We introduce and study families of finite index subgroups of the modular group that generalize the congruence subgroups. Such groups, termed ϕ‐congruence subgroups, are obtained by reducing homomorphisms ϕ from the modular group into a linear algebraic group modulo integers. In particular, we examine two families of examples, arising on the one hand from a map into a quasi‐unipotent group, and on the other hand from maps into symplectic groups of degree four. In the quasi‐unipotent case, we also provide a detailed discussion of the corresponding modular forms, using the fact that the tower of curves in this case contains the tower of isogenies over the elliptic curve y2=x3−1728$y^2=x^3-1728$ defined by the commutator subgroup of the modular group.","PeriodicalId":18463,"journal":{"name":"Mathematika","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1112/mtk.12218","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45504633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
MathematikaPub Date : 2023-08-10DOI: 10.1112/mtk.12219
Peng Gao, Liangyi Zhao
{"title":"Lower bounds for negative moments of \u0000 \u0000 \u0000 \u0000 ζ\u0000 ′\u0000 \u0000 \u0000 (\u0000 ρ\u0000 )\u0000 \u0000 \u0000 $zeta ^{prime }(rho )$","authors":"Peng Gao, Liangyi Zhao","doi":"10.1112/mtk.12219","DOIUrl":"10.1112/mtk.12219","url":null,"abstract":"<p>We establish lower bounds for the discrete 2<i>k</i>th moment of the derivative of the Riemann zeta function at nontrivial zeros for all <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>k</mi>\u0000 <mo><</mo>\u0000 <mn>0</mn>\u0000 </mrow>\u0000 <annotation>$k<0$</annotation>\u0000 </semantics></math> under the Riemann hypothesis and the assumption that all zeros of <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>ζ</mi>\u0000 <mo>(</mo>\u0000 <mi>s</mi>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 <annotation>$zeta (s)$</annotation>\u0000 </semantics></math> are simple.</p>","PeriodicalId":18463,"journal":{"name":"Mathematika","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1112/mtk.12219","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42508800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}