{"title":"DW-DP operators and DW-limited operators on Banach lattices","authors":"Jin Xi Chen, Jingge Feng","doi":"10.1007/s43036-025-00429-x","DOIUrl":"10.1007/s43036-025-00429-x","url":null,"abstract":"<div><p>This paper is devoted to the study of two classes of operators related to disjointly weakly compact sets, which we call <i>DW</i>-DP operators and <i>DW</i>-limited operators, respectively. They carry disjointly weakly compact sets in a Banach lattice onto Dunford–Pettis sets and limited sets, respectively. We show that <i>DW</i>-DP (resp. <i>DW</i>-limited) operators are precisely those operators which are both weak Dunford–Pettis and order Dunford–Pettis (resp. weak<span>(^*)</span> Dunford–Pettis and order limited) operators. Furthermore, the approximation properties of positive <i>DW</i>-DP and positive <i>DW</i>-limited operators are given.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-025-00429-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143581144","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Chernoff’s product formula: Semigroup approximations with non-uniform time intervals","authors":"József Zsolt Bernád, Andrew B. Frigyik","doi":"10.1007/s43036-025-00428-y","DOIUrl":"10.1007/s43036-025-00428-y","url":null,"abstract":"<div><p>Often, when we consider the time evolution of a system, we resort to approximation: Instead of calculating the exact orbit, we divide the time interval in question into uniform segments. Chernoff’s results in this direction provide us with a general approximation scheme. There are situations when we need to break the interval into uneven pieces. In this paper, we explore alternative conditions to the one found by Smolyanov <i>et al</i>. such that Chernoff’s original result can be extended to unevenly distributed time intervals. Two applications concerning the foundations of quantum mechanics and the central limit theorem are presented.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-025-00428-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143527628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Paired kernels and truncated Toeplitz operators","authors":"M. Cristina Câmara, Jonathan R. Partington","doi":"10.1007/s43036-025-00426-0","DOIUrl":"10.1007/s43036-025-00426-0","url":null,"abstract":"<div><p>This paper considers paired operators in the context of the Lebesgue Hilbert space <span>(L^2)</span> on the unit circle and its subspace, the Hardy space <span>(H^2.)</span> The kernels of such operators, together with their analytic projections, which are generalizations of Toeplitz kernels, are studied. Inclusion relations between such kernels are considered in detail, and the results are applied to describing the kernels of finite-rank asymmetric truncated Toeplitz operators.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-025-00426-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143496980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Tingley’s problem for the direct sum of uniformly closed extremely C-regular subspaces with the (ell ^{1})-sum norm","authors":"Daisuke Hirota","doi":"10.1007/s43036-025-00427-z","DOIUrl":"10.1007/s43036-025-00427-z","url":null,"abstract":"<div><p>Tingley’s problem asks whether every surjective isometry between two unit spheres of Banach spaces can be extended to a surjective real linear isometry between the whole spaces. Let <span>({A_mu }_{mu in M})</span> and <span>({A_{nu }}_{nu in N})</span> be two collections of uniformly closed extremely C-regular subspaces. In this paper, we prove that if <span>(Delta )</span> is a surjective isometry between two unit spheres of <span>(ell ^1)</span>-sums of uniformly closed extremely C-regular subspaces <span>({A_{mu }}_{mu in M})</span> and <span>({A_{nu }}_{nu in N})</span>, then <span>(Delta )</span> admits an extension to a surjective real linear isometry between the whole spaces. Typical examples of such Banach spaces <i>B</i> are <span>(C^1(I))</span> of all continuously differentiable complex-valued functions on the closed unit interval <i>I</i> equipped with the norm <span>(Vert fVert _{1}=|f(0)|+Vert f'Vert _{infty })</span> for <span>(fin C^1(I))</span>, <span>(C^{(n)}(I))</span> of all <i>n</i>-times continuously differentiable complex-valued functions on <i>I</i> with the norm <span>(Vert fVert _{1}=sum _{k=0}^{n-1}|f^{(k)}(0)|+~Vert f^{(n)}Vert _{infty })</span> for <span>(C^{n}(I))</span>, and <span>(ell ^1(mathbb {N}))</span> of all complex-valued functions on the set <span>(mathbb {N})</span> of all natural numbers with the norm <span>(Vert aVert _{1}=sum _{nin mathbb {N}}|a(n)|)</span> for <span>(ain ell ^1(mathbb {N}))</span>.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143489488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Application of operator theory for the collatz conjecture","authors":"Takehiko Mori","doi":"10.1007/s43036-025-00425-1","DOIUrl":"10.1007/s43036-025-00425-1","url":null,"abstract":"<div><p>The Collatz map (or the <span>(3n{+}1)</span>-map) <i>f</i> is defined on positive integers by setting <i>f</i>(<i>n</i>) equal to <span>(3n+1)</span> when <i>n</i> is odd and <i>n</i>/2 when <i>n</i> is even. The Collatz conjecture states that starting from any positive integer <i>n</i>, some iterate of <i>f</i> takes value 1. In this study, we discuss formulations of the Collatz conjecture by <span>(C^{*})</span>-algebras in the following three ways: (1) single operator, (2) two operators, and (3) Cuntz algebra. For the <span>(C^{*})</span>-algebra generated by each of these, we consider the condition that it has no non-trivial reducing subspaces. For (1), we prove that the condition implies the Collatz conjecture. In the cases (2) and (3), we prove that the condition is equivalent to the Collatz conjecture. For similar maps, we introduce equivalence relations by them and generalize connections between the Collatz conjecture and irreducibility of associated <span>(C^{*})</span>-algebras.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143455699","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Comparing the ill-posedness for linear operators in Hilbert spaces","authors":"Peter Mathé, Bernd Hofmann","doi":"10.1007/s43036-025-00422-4","DOIUrl":"10.1007/s43036-025-00422-4","url":null,"abstract":"<div><p>The difficulty for solving ill-posed linear operator equations in Hilbert space is reflected by the strength of ill-posedness of the governing operator, and the inherent solution smoothness. In this study we focus on the ill-posedness of the operator, and we propose a partial ordering for the class of all bounded linear operators which lead to ill-posed operator equations. For compact linear operators, there is a simple characterization in terms of the decay rates of the singular values. In the context of the validity of the spectral theorem the partial ordering can also be understood. We highlight that range inclusions yield partial ordering, and we discuss cases when compositions of compact and non-compact operators occur. Several examples complement the theoretical results.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143430995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Using the Baire category theorem to explore Lions problem for quasi-Banach spaces","authors":"A. G. Aksoy, J. M. Almira","doi":"10.1007/s43036-025-00423-3","DOIUrl":"10.1007/s43036-025-00423-3","url":null,"abstract":"<div><p>Many results for Banach spaces also hold for quasi-Banach spaces. One important such example is results depending on the Baire category theorem (BCT). We use the BCT to explore Lions problem for a quasi-Banach couple <span>((A_0, A_1).)</span> Lions problem, posed in 1960s, is to prove that different parameters <span>((theta ,p))</span> produce different interpolation spaces <span>((A_0, A_1)_{theta , p}.)</span> We first establish conditions on <span>(A_0)</span> and <span>(A_1)</span> so that interpolation spaces of this couple are strictly intermediate spaces between <span>(A_0+A_1)</span> and <span>(A_0cap A_1.)</span> This result, together with a reiteration theorem, gives a partial solution to Lions problem for quasi-Banach couples. We then apply our interpolation result to (partially) answer a question posed by Pietsch. More precisely, we show that if <span>(pne p^*)</span> the operator ideals <span>({mathcal {L}}^{(a)}_{p,q}(X,Y),)</span> <span>({mathcal {L}}^{(a)}_{p^*,q^*}(X,Y))</span> generated by approximation numbers are distinct. Moreover, for any fixed <i>p</i>, either all operator ideals <span>({mathcal {L}}^{(a)}_{p,q}(X,Y))</span> collapse into a unique space or they are pairwise distinct. We cite counterexamples which show that using interpolation spaces is not appropriate to solve Pietsch’s problem for operator ideals based on general <i>s</i>-numbers. However, the BCT can be used to prove a lethargy result for arbitrary <i>s</i>-numbers which guarantees that, under very minimal conditions on <i>X</i>, <i>Y</i>, the space <span>({mathcal {L}}^{(s)}_{p,q}(X,Y))</span> is strictly embedded into <span>({mathcal {L}}^{mathcal {A}}(X,Y).)</span></p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-025-00423-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143423476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tanise Carnieri Pierin, Ruth Nascimento Ferreira, Fernando Borges, Bruno Leonardo Macedo Ferreira
{"title":"About the additivity of a nonlinear mixed (*)-Jordan type derivation defined on an alternative (*)-algebra","authors":"Tanise Carnieri Pierin, Ruth Nascimento Ferreira, Fernando Borges, Bruno Leonardo Macedo Ferreira","doi":"10.1007/s43036-025-00424-2","DOIUrl":"10.1007/s43036-025-00424-2","url":null,"abstract":"<div><p>For an alternative <span>(*)</span>-algebra <i>A</i> under some additional hypothesis, we prove that a map from <i>A</i> into itself is a nonlinear mixed <span>(*)</span>-Jordan type derivation if and only is an additive <span>(*)</span>-derivation. As consequence, some results on the complex octonion algebra, associative <span>(*)</span>-algebras, and <span>(W^*)</span>-factor algebras were obtained.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143423475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Commuting families of polygonal type operators on Hilbert space","authors":"Christian Le Merdy, M. N. Reshmi","doi":"10.1007/s43036-024-00407-9","DOIUrl":"10.1007/s43036-024-00407-9","url":null,"abstract":"<div><p>Let <span>(T:Hrightarrow H)</span> be a bounded operator on Hilbert space <i>H</i>. We say that <i>T</i> has a polygonal type if there exists an open convex polygon <span>(Delta subset {mathbb {D}})</span>, with <span>(overline{Delta }cap {mathbb {T}}ne emptyset )</span>, such that the spectrum <span>(sigma (T))</span> is included in <span>(overline{Delta })</span> and the resolvent <i>R</i>(<i>z</i>, <i>T</i>) satisfies an estimate <span>(Vert R(z,T)Vert lesssim max {vert z-xi vert ^{-1},:, xi in overline{Delta }cap {mathbb {T}}})</span> for <span>(zin overline{mathbb {D}}^c)</span>. The class of polygonal type operators (which goes back to De Laubenfels and Franks–McIntosh) contains the class of Ritt operators. Let <span>(T_1,ldots ,T_d)</span> be commuting operators on <i>H</i>, with <span>(dge 3)</span>. We prove functional calculus properties of the <i>d</i>-tuple <span>((T_1,ldots ,T_d))</span> under various assumptions involving poygonal type. The main ones are the following. (1) If the operator <span>(T_k)</span> is a contraction for all <span>(k=1,ldots ,d)</span> and if <span>(T_1,ldots ,T_{d-2})</span> have a polygonal type, then <span>((T_1,ldots ,T_d))</span> satisfies a generalized von Neumann inequality <span>(Vert phi (T_1,ldots ,T_d)Vert le CVert phi Vert _{infty ,{mathbb {D}}^d})</span> for polynomials <span>(phi )</span> in <i>d</i> variables; (2) If <span>(T_k)</span> is polynomially bounded with a polygonal type for all <span>(k=1,ldots ,d)</span>, then there exists an invertible operator <span>(S:Hrightarrow H)</span> such that <span>(Vert S^{-1}T_kSVert le 1)</span> for all <span>(k=1,ldots ,d)</span>.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143361809","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Aspects of equivariant KK-theory in its generators and relations picture","authors":"Bernhard Burgstaller","doi":"10.1007/s43036-024-00412-y","DOIUrl":"10.1007/s43036-024-00412-y","url":null,"abstract":"<div><p>We consider the universal additive category derived from the category of equivariant separable <span>(C^*)</span>-algebras by introducing homotopy invariance, stability and split-exactness. We show that morphisms in that category permit a particular simple form, thus obtaining the universal property of <span>(KK^G)</span>-theory for <i>G</i> a locally compact group, or a locally compact groupoid with compact base space, or a countable inverse semigroup as a byproduct.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"10 2","pages":""},"PeriodicalIF":0.8,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143107805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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