{"title":"Mixed \u0000 \u0000 \u0000 L\u0000 p\u0000 \u0000 $L^p$\u0000 estimates for transforms of noncommutative martingales","authors":"Adam Osękowski","doi":"10.1112/blms.13184","DOIUrl":"https://doi.org/10.1112/blms.13184","url":null,"abstract":"<p>Let <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>1</mn>\u0000 <mo><</mo>\u0000 <mi>p</mi>\u0000 <mo><</mo>\u0000 <mspace></mspace>\u0000 <mi>q</mi>\u0000 <mo><</mo>\u0000 <mi>∞</mi>\u0000 </mrow>\u0000 <annotation>$1<p<, q<infty $</annotation>\u0000 </semantics></math>. The paper is devoted to the study of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mi>L</mi>\u0000 <mi>q</mi>\u0000 </msup>\u0000 <mo>→</mo>\u0000 <msup>\u0000 <mi>L</mi>\u0000 <mi>p</mi>\u0000 </msup>\u0000 </mrow>\u0000 <annotation>$L^qrightarrow L^p$</annotation>\u0000 </semantics></math> estimates for transforms of noncommutative martingales, under the assumption that the transforming sequence takes values in <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mi>L</mi>\u0000 <mi>r</mi>\u0000 </msup>\u0000 <annotation>$L^r$</annotation>\u0000 </semantics></math>, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>1</mn>\u0000 <mo>/</mo>\u0000 <mi>r</mi>\u0000 <mo>=</mo>\u0000 <mn>1</mn>\u0000 <mo>/</mo>\u0000 <mi>p</mi>\u0000 <mo>−</mo>\u0000 <mn>1</mn>\u0000 <mo>/</mo>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 <annotation>$1/r=1/p-1/q$</annotation>\u0000 </semantics></math>. This goes beyond the usual context of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>p</mi>\u0000 <mo>=</mo>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 <annotation>$p=q$</annotation>\u0000 </semantics></math> and <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>r</mi>\u0000 <mo>=</mo>\u0000 <mi>∞</mi>\u0000 </mrow>\u0000 <annotation>$r=infty$</annotation>\u0000 </semantics></math> studied so far in the literature. The obtained constants are of optimal order at the endpoints, in addition the approach allows to obtain sharp values in the range <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>p</mi>\u0000 <mo>⩽</mo>\u0000 <mn>2</mn>\u0000 <mo>⩽</mo>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 <annotation>$pleqslant 2leqslant q$</annotation>\u0000 </semantics></math>. The proof rests on real interpolation-type arguments for martingale transforms, which are of independent interest.</p>","PeriodicalId":55298,"journal":{"name":"Bulletin of the London Mathematical Society","volume":"57 1","pages":"96-114"},"PeriodicalIF":0.8,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143114395","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}