{"title":"Interpolating sequences for weighted spaces of analytic functions on Banach spaces","authors":"Mario P. Maletzki","doi":"10.1007/s43036-026-00505-w","DOIUrl":"10.1007/s43036-026-00505-w","url":null,"abstract":"<div><p>Given a weight <i>v</i> on an open set <i>G</i> of a Banach space <i>E</i>, the weighted spaces of analytic functions <i>Hv</i>(<i>G</i>) and <span>(Hv_0(G))</span> and their interpolating sequences are studied. In particular, it is shown that for a large class of weights on <span>(B_E)</span> we have that <i>Hv</i>(<i>G</i>) is naturally isometrically isomorphic to <span>(Hv_0(G)^{**})</span>, and that for those weights the interpolating sequences for <span>(Hv(B_E))</span> are completely classified by their boundary behavior either as the interpolating sequences for <span>(Hv_0(B_E))</span> or for the classical Hardy space <span>(H^infty (B_E))</span>.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 3","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147829247","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":"Rapid decay for odometers","authors":"Slawomir Klimek, Matt McBride","doi":"10.1007/s43036-026-00508-7","DOIUrl":"10.1007/s43036-026-00508-7","url":null,"abstract":"<div><p>We discuss rapid decay functions on odometer Cantor spaces and their noncommutative geometry applications.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 3","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147829391","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}
M. R. Marcial, L. C. Paes-Leme, E. M. Martins, W. M. Ferreira
{"title":"Infinitely many solutions for a class of fractional Kirchhoff problems with critical exponent","authors":"M. R. Marcial, L. C. Paes-Leme, E. M. Martins, W. M. Ferreira","doi":"10.1007/s43036-026-00506-9","DOIUrl":"10.1007/s43036-026-00506-9","url":null,"abstract":"<div><p>We study a class of nonlocal Kirchhoff-type problems involving the fractional <span>( p )</span>-Laplacian and critical Sobolev growth. The equation includes a Kirchhoff term <span>( M(t) = a + t^m )</span>, with <span>( a ge 0 )</span> and <span>( m > 0 )</span>, and is posed on a bounded domain with Lipschitz boundary. Using variational methods, Krasnoselskii’s genus theory, and a fractional concentration-compactness principle, we prove the existence of infinitely many weak solutions in both the non-degenerate (<span>( a > 0 )</span>) and degenerate (<span>( a = 0 )</span>) cases.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 3","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-026-00506-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147756001","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":"On the idempotent operator and polar decomposition","authors":"Chunyuan Deng, Xingxue Fu, Xiaohui Li","doi":"10.1007/s43036-025-00491-5","DOIUrl":"10.1007/s43036-025-00491-5","url":null,"abstract":"<div><p>Suppose <i>Q</i> is an idempotent operator. Let <span>(Q=V_Q|Q|)</span> and <span>(Psi =U_Psi |Psi |)</span> be the polar decompositions of <i>Q</i> and <span>(Psi =2Q-I)</span>, respectively. Let <span>(Phi =Q+Q^*)</span> and <span>(Upsilon =Q+Q^*-I)</span>. We prove that <span>(Q=|Q^*||Q|=frac{1}{2}big [(2|Phi |-|Psi |)U_{Psi } -Ibig ],)</span> <span>(|Phi |=|Q|+|Q^*|= |Upsilon |+ U_{Psi },)</span> <span>( |Q|-|Q^*|=frac{1}{2}(|Psi |-|Psi ^*|)=|Psi |-|Upsilon |=|Upsilon |-|Psi ^*|)</span> and <span>(U_{Psi }= U^*_{Psi }= U^{-1}_{Psi }=|Psi |Psi =|Psi ^*|Psi ^*=Psi |Psi ^*| =Psi ^*|Psi |=|Upsilon |Upsilon ^{-1}=|Upsilon |^{-1}Upsilon .)</span> The equivalent conditions for positive operators <i>A</i> and <i>B</i> which can be written as <span>(A=Q^*Q)</span> and <span>(B=QQ^*)</span> are obtained. Also, we characterize the idempotents <i>Q</i>, <span>(Q_1)</span> and <span>(Q_2)</span> such that <span>({mathcal {R}}(Q) subseteq {mathcal {R}}(Q_1))</span> or <span>( {mathcal {N}}(Q_2) subseteq {mathcal {N}}(Q))</span>. In particular, the equivalent condition for idempotent <i>Q</i> which can be written as the product <span>(Q=Q_1Q_2)</span> is described.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147737471","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":"Small representations associated with Heisenberg Gelfand pairs","authors":"Aymen Rahali, Sofien Hamdani","doi":"10.1007/s43036-026-00504-x","DOIUrl":"10.1007/s43036-026-00504-x","url":null,"abstract":"<div><p>Let <span>((K,H_V))</span> be a Heisenberg Gelfand pair and <span>(G:=Kltimes H_V)</span> be its associated semidirect product. Here, <i>K</i> is a compact Lie group acting smoothly on the Heisenberg group <span>(H_V:=Vtimes mathbb {R},)</span> where <i>V</i> is a finite-dimensional complex vector space. Let <span>(widehat{G})</span> be the unitary dual of <i>G</i> equipped with the Fell topology. We say that <span>(pi in widehat{G})</span> is a <i>spherical representation</i> of <i>G</i> if the restriction <span>(pi |_K)</span> of <span>(pi )</span> to the subgroup <i>K</i> has a one-dimensional space of <i>K</i>-fixed vectors. Boidol, Ludwig and Müller have introduced the notion of the so-called <i>small representations</i> of <i>G</i>, that is all <span>(pi in widehat{G})</span> that cannot be Hausdorff separated from the trivial one-dimensional representation <span>(1_G)</span> of <i>G</i>. Using a parametrization of the set of irreducible spherical representations due to work of Benson-Ratcliff, we show that any non-trivial spherical representation of <i>G</i> cannot be a small representation. Furthermore, we prove that the converse of this statement is false in the setting of the Heisenberg motion group <span>(G_d:=U(d)ltimes H_{mathbb {C}^d}, din mathbb {N}^times .)</span></p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147642454","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":"Pullback attractors of non-autonomous nonclassical diffusion equations with state-dependent delay","authors":"Qiaozhen Ma, Tongtong Liang, Wenting Liu","doi":"10.1007/s43036-026-00498-6","DOIUrl":"10.1007/s43036-026-00498-6","url":null,"abstract":"<div><p>In this paper, we investigate the existence of pullback attractors for a non-autonomous nonclassical diffusion equation with state-dependent delay. First, the existence and uniqueness of strong solutions are proved via the standard Faedo-Galerkin method. To address the state-dependent delay, we incorporate its compensator into a normal functional, which enables us to obtain both the existence of a pullback absorbing set and the pullback asymptotic compactness of the corresponding evolution process. In particular, new properties of specific composition operators are derived to support the main results. Finally, we establish the existence of pullback attractors.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147642487","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":"Frame dimension functions of g-frames","authors":"Tian Wang, Miao He","doi":"10.1007/s43036-026-00502-z","DOIUrl":"10.1007/s43036-026-00502-z","url":null,"abstract":"<div><p>Frame theory has important applications in phase-retrieval problem, and the dimension function of a frame can serve as a candidate for measuring its phase retrievability. In this paper, we first investigate the relationship between phase retrievability and the dimension function of g-frames incorporating operator theory. We find that the dimension function of a phase-retrievable g-frame closely aligns with that of an ordinary frame. This consistency suggests that the dimension function of a g-frame can likewise act as a metric for measuring its phase retrieval capability. Specifically, we find that the exact PR-redundancy of a g-frame is equivalent to the exactness of its dimension function. The paper then investigates the structure of the dimension function range of g-frames. We find that, even when the number of operators in a g-frame is not less than <i>n</i>, significant differences remain from the case of ordinary frames regarding the structure of the dimension function range of g-Riesz basis and whether the range contains <i>n</i>. Finally, we present a method for examining the dimension function of a g-frame via its induced frame, along with a straightforward approach to construct g-frames whose dimension function range contains <i>n</i>.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147642412","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}
Itzama Delgadillo-García, Rubén A. Martínez-Avendaño
{"title":"The forward and backward shift on the Zygmund space of a tree","authors":"Itzama Delgadillo-García, Rubén A. Martínez-Avendaño","doi":"10.1007/s43036-026-00501-0","DOIUrl":"10.1007/s43036-026-00501-0","url":null,"abstract":"<div><p>The Zygmund space of a tree is the Banach space of complex-valued functions defined on the vertices of a rooted infinite and locally-finite tree such that their second discrete derivative is bounded. In this paper we study the forward and backward shift operators on the Zygmund space of a tree. We show that the forward shift operator is always bounded on the Zygmund space, and we find its norm and spectrum. We give necessary and sufficient conditions for the backward shift operator to be bounded, and give an estimate for its norm. In the case the tree is homogeneous, we give an exact expression for the norm of the backward shift operator and we find its spectrum. The results in the paper also apply verbatim to the little Zygmund space.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147607007","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":"A complete asymptotic expansion for the semi-exponential Post–Widder operators","authors":"Ulrich Abel, Octavian Agratini, Radu Păltănea","doi":"10.1007/s43036-026-00499-5","DOIUrl":"10.1007/s43036-026-00499-5","url":null,"abstract":"<div><p>In the present paper, we study the asymptotic properties of the semi-exponential Post–Widder operator. It is connected with the power function <i>p</i>, <span>(pleft( xright) =x^{2})</span>. The main result is a pointwise complete asymptotic expansion valid for locally smooth functions of exponential growth. All coefficients are derived and explicitly given. As a special case we recover the complete asymptotic expansion for the classical Post–Widder operator.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s43036-026-00499-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147561640","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":"Local symmetry and smoothness in the space of vector-valued continuous functions","authors":"Mohit, Ranjana Jain","doi":"10.1007/s43036-026-00500-1","DOIUrl":"10.1007/s43036-026-00500-1","url":null,"abstract":"<div><p>In this article, we characterize the left symmetric points in <i>C</i>(<i>K</i>, <i>X</i>), where <i>K</i> is a compact Hausdorff space and <i>X</i> is a Banach space. We also provide necessary and sufficient conditions for the right symmetric points in <i>C</i>(<i>K</i>, <i>X</i>). Further, we identify the smooth points in the space <span>(C_0(K,X))</span>, <i>K</i> being locally compact Hausdorff space and <i>X</i> being a Banach space.</p></div>","PeriodicalId":44371,"journal":{"name":"Advances in Operator Theory","volume":"11 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147559753","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}