{"title":"A sharp estimate of area for sublevel-set of Blaschke products","authors":"David Kalaj","doi":"arxiv-2407.19539","DOIUrl":null,"url":null,"abstract":"Let $\\mathbb{D}$ be the unit disk in the complex plane. Among other results,\nwe prove the following curious result for a finite Blaschke product: $$B(z)=e\n^{is}\\prod_{k=1}^d \\frac{z-a_k}{1-z \\overline{a_k}}.$$ The Lebesgue measure of\nthe sublevel set of $B$ satisfies the following sharp inequality for $t \\in\n[0,1]$: $$|\\{z\\in \\mathbb{D}:|B(z)|<t\\}|\\le \\pi t^{2/d},$$ with equality at a\nsingle point $t\\in(0,1)$ if and only if $a_k=0$ for every $k$. In that case the\nequality is attained for every $t$.","PeriodicalId":501142,"journal":{"name":"arXiv - MATH - Complex Variables","volume":"50 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - MATH - Complex Variables","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2407.19539","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Let $\mathbb{D}$ be the unit disk in the complex plane. Among other results,
we prove the following curious result for a finite Blaschke product: $$B(z)=e
^{is}\prod_{k=1}^d \frac{z-a_k}{1-z \overline{a_k}}.$$ The Lebesgue measure of
the sublevel set of $B$ satisfies the following sharp inequality for $t \in
[0,1]$: $$|\{z\in \mathbb{D}:|B(z)|