{"title":"On the invertibility of bounded operators with a lower bound on reflexive Banach spaces, and applications to (C_{0})-semigroups","authors":"Belabbas Madani","doi":"10.1007/s00013-025-02209-8","DOIUrl":"10.1007/s00013-025-02209-8","url":null,"abstract":"<div><p>We present a new version of an invertibility result for operators satisfying a lower bound condition. The result states that any bounded operator on a reflexive Banach space, which satisfies the lower bound condition, can be extended to a larger reflexive Banach space where it becomes invertible. Furthermore, we provide applications to <span>(C_{0})</span>-semigroups.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 3","pages":"305 - 313"},"PeriodicalIF":0.5,"publicationDate":"2026-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147337118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Newly appointed editors","authors":"","doi":"10.1007/s00013-025-02203-0","DOIUrl":"10.1007/s00013-025-02203-0","url":null,"abstract":"","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 1","pages":"1 - 1"},"PeriodicalIF":0.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Local (L^2)-boundedness of rough Fourier integral operators with the rough corank condition","authors":"Xiao Yu, Xiangrong Zhu","doi":"10.1007/s00013-025-02207-w","DOIUrl":"10.1007/s00013-025-02207-w","url":null,"abstract":"<div><p>In this paper, we consider a rough Fourier integral operator defined as </p><div><div><span>$$T_{phi ,a}f(x)=int limits _{mathbb {R}^{n}}e^{iphi (x,xi )}a(x,xi )hat{f}(xi )dxi ,$$</span></div></div><p>where the amplitude <span>(ain L^{infty }S^{m}_{rho })</span> and the phase <span>(phi in L^{infty }Phi ^{2})</span> satisfy the rough <i>k</i>-corank condition. The motivation for this problem stems from the regularity of the maximal wave operator. We prove that this operator is bounded from <span>(L^{2})</span> to <span>(L_{text {loc}}^{2})</span> provided </p><div><div><span>$$m<min left{ frac{n(rho -1)}{2},frac{rho }{2}-frac{n+1}{4}right} -frac{krho }{2}.$$</span></div></div></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 3","pages":"315 - 327"},"PeriodicalIF":0.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147337028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Image ratios of word maps and polynomial maps","authors":"Saikat Panja","doi":"10.1007/s00013-025-02194-y","DOIUrl":"10.1007/s00013-025-02194-y","url":null,"abstract":"<div><p>Let <i>A</i> be a finite group (or a finite algebra), and <span>(omega )</span> be a word map (resp. polynomial map) on <i>n</i> many generators. We define the quantity <span>(|omega (A)|/|A|)</span> as the <i>image ratio of</i> <span>(omega )</span> <i>on</i> <i>A</i> and denote it by <span>(mu (omega ,A))</span>. In this article, we investigate the set <span>(textrm{R}(omega )={mu (omega , A) : A {text { is a finite group}}})</span>, and study the same for the case of rings. We demonstrate the existence of word maps whose set of image ratios is dense in [0, 1] for groups (and rings).</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 1","pages":"21 - 28"},"PeriodicalIF":0.5,"publicationDate":"2025-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969471","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A note on singularity indices of hyperelliptic fibrations","authors":"Cheng Gong, Zhiming Guo, Xin Lü","doi":"10.1007/s00013-025-02198-8","DOIUrl":"10.1007/s00013-025-02198-8","url":null,"abstract":"<div><p>Let <span>(f: X rightarrow B)</span> be a relatively minimal hyperelliptic fibration of genus <i>g</i>. For such a fibration <i>f</i>, Xiao introduced a series of singularity indices <span>(s_i(f))</span> for <span>(2le i le g+2)</span>. These indices provide an effective way to study the geometry of <i>f</i>. It is known that <span>(s_i(f)ge 0)</span> for <span>(ige 3)</span>, but it is not clear whether <span>(s_2(f))</span> is non-negative. In this note, we construct a sequence of hyperelliptic fibrations with <span>(s_2(f)<0)</span>, where the genus <i>g</i> can be arbitrarily large.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 2","pages":"153 - 163"},"PeriodicalIF":0.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147335971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Tor algebra of local rings with decomposable maximal ideal","authors":"Saeed Nasseh, Maiko Ono, Yuji Yoshino","doi":"10.1007/s00013-025-02200-3","DOIUrl":"10.1007/s00013-025-02200-3","url":null,"abstract":"<div><p>Let <span>((R,mathfrak {m}_R))</span> be a commutative noetherian local ring. Assuming that <span>(mathfrak {m}_R=Ioplus J)</span> is a direct sum decomposition, where <i>I</i> and <i>J</i> are non-zero ideals of <i>R</i>, we describe the structure of the Tor algebra of <i>R</i> in terms of the Tor algebras of the rings <i>R</i>/<i>I</i> and <i>R</i>/<i>J</i>.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 2","pages":"127 - 137"},"PeriodicalIF":0.5,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147342384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Concentration of norms of random vectors with independent p-sub-exponential coordinates","authors":"Krzysztof Zajkowski","doi":"10.1007/s00013-025-02199-7","DOIUrl":"10.1007/s00013-025-02199-7","url":null,"abstract":"<div><p>We present examples of <i>p</i>-sub-exponential random variables for any positive <i>p</i>. We prove two types of concentration of standard <i>p</i>-norms (2-norm is the Euclidean norm) of random vectors with independent <i>p</i>-sub-exponential coordinates around the Lebesgue <span>(L^p)</span>-norms of these <i>p</i>-norms of random vectors. In the first case <span>(pge 1)</span>, our estimates depend on the dimension <i>n</i> of random vectors. But in the second one for <span>(pge 2)</span>, with an additional assumption, we get an estimate that does not depend on <i>n</i>. In other words, we generalize some known concentration results in the Euclidean case to cases of the <i>p</i>-norms of random vectors with independent <i>p</i>-sub-exponential coordinates.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 2","pages":"209 - 220"},"PeriodicalIF":0.5,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00013-025-02199-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147342544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Lie product type formulas for the logarithm","authors":"Dumitru Popa","doi":"10.1007/s00013-025-02201-2","DOIUrl":"10.1007/s00013-025-02201-2","url":null,"abstract":"<div><p>In this paper, we prove various Lie product type formulas for the logarithm. A sample result: Let <span>(kge 2)</span> be a natural number, <span>(X_{1})</span>,..., <span>(X_{k})</span>, <i>Y</i> Banach algebras with unit and <span>(T:X_{1}times cdot cdot cdot times X_{k}rightarrow Y)</span> a continuous <i>k</i>-linear operator such that <span>(Tleft( textbf{1},...,textbf{1}right) =textbf{1})</span>. Let <span>(left( a_{n}right) _{nin mathbb {N}})</span> be a sequence of natural numbers with <span>( lim _{nrightarrow infty }a_{n}=infty )</span>. Then for all <span>(left( x_{1},...,x_{k}right) in X_{1}times cdot cdot cdot times X_{k})</span> we have </p><div><div><span>$$begin{aligned} & lim limits _{nrightarrow infty }left[ Tleft( textbf{1}+ln left( textbf{1}+frac{x_{1}}{a_{n}}right) ,...,textbf{1}+ln left( textbf{1}+ frac{x_{k}}{a_{n}}right) right) right] ^{a_{n}} & quad =e^{Tleft( x_{1},textbf{1},...,textbf{1}right) +Tleft( textbf{1},x_{2},textbf{1},...,textbf{1}right) +cdot cdot cdot +Tleft( textbf{1},...,textbf{1},x_{k}right) }. end{aligned}$$</span></div></div></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 2","pages":"177 - 186"},"PeriodicalIF":0.5,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147342383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Stability estimate for an inverse potential problem in time-fractional diffusion problem","authors":"Hamza Kahlaoui","doi":"10.1007/s00013-025-02185-z","DOIUrl":"10.1007/s00013-025-02185-z","url":null,"abstract":"<div><p>We investigate the inverse problem of identifying a space-depen- dent potential in a Caputo time-fractional diffusion equation from boundary observations. Our analysis establishes a maximum principle for subdiffusion equations with non-homogeneous Neumann boundary conditions, demonstrating the positivity of solutions under specific assumptions on the boundary data. Building upon this result, we leverage the Gâteaux differentiability of the forward map and the non-vanishing property of its derivative to derive a local Lipschitz stability estimate for the inverse potential problem. This provides a rigorous foundation for the stable reconstruction of the potential, highlighting the interplay between fractional dynamics and stability in inverse problems.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 1","pages":"87 - 105"},"PeriodicalIF":0.5,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969474","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The median trick does not help for fully nested scrambling","authors":"Takashi Goda, Kosuke Suzuki","doi":"10.1007/s00013-025-02205-y","DOIUrl":"10.1007/s00013-025-02205-y","url":null,"abstract":"<div><p>In randomized quasi-Monte Carlo methods for numerical integration, average estimators based on digital nets with fully nested and linear scramblings, respectively, are known to exhibit the same variance. In this note, we show that this equivalence does not extend to the median estimators. Specifically, while the median estimator with linear scrambling can achieve faster convergence for smooth integrands, the median estimator with fully nested scrambling does not exhibit this advantage.</p></div>","PeriodicalId":8346,"journal":{"name":"Archiv der Mathematik","volume":"126 2","pages":"221 - 230"},"PeriodicalIF":0.5,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147342315","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}