{"title":"LINEAR PRESERVERS ON IDEMPOTENTS OF FOURIER ALGEBRAS","authors":"Ying-Fen Lin, Shiho Oi","doi":"10.4153/s0008439523000395","DOIUrl":"https://doi.org/10.4153/s0008439523000395","url":null,"abstract":"In this article, we give a representation of bounded complex linear operators which preserve idempotent elements on the Fourier algebra of a locally compact group. When such an operator is moreover positive or contractive, we show that the operator is induced by either a continuous group homomorphism or a continuous group anti-homomorphism. If the groups are totally disconnected, bounded homomorphisms on the Fourier algebra can be realised by the idempotent preserving operators.","PeriodicalId":55280,"journal":{"name":"Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques","volume":null,"pages":null},"PeriodicalIF":0.6,"publicationDate":"2023-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47254819","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":"Erdős–Ko–Rado theorem in Peisert-type graphs","authors":"Chi Hoi Yip","doi":"10.4153/S0008439523000607","DOIUrl":"https://doi.org/10.4153/S0008439523000607","url":null,"abstract":"The celebrated ErdH{o}s-Ko-Rado (EKR) theorem for Paley graphs (of square order) states that all maximum cliques are canonical in the sense that each maximum clique arises from the subfield construction. Recently, Asgarli and Yip extended this result to Peisert graphs and other Cayley graphs which are Peisert-type graphs with nice algebraic properties on the connection set. On the other hand, there are Peisert-type graphs for which the EKR theorem fails to hold. In this paper, we show that the EKR theorem of Paley graphs extends to almost all pseudo-Paley graphs of Peisert-type. Furthermore, we establish the stability results of the same flavor.","PeriodicalId":55280,"journal":{"name":"Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques","volume":null,"pages":null},"PeriodicalIF":0.6,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41959603","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":"Bohr–Rogosinski radius for a certain class of close-to-convex harmonic mappings","authors":"MOLLA BASIR AHAMED, VASUDEVARAO ALLU","doi":"10.4153/s0008439523000115","DOIUrl":"https://doi.org/10.4153/s0008439523000115","url":null,"abstract":"Abstract Let \u0000$ mathcal {B} $\u0000 be the class of analytic functions \u0000$ f $\u0000 in the unit disk \u0000$ mathbb {D}={zin mathbb {C} : |z|<1} $\u0000 such that \u0000$ |f(z)|<1 $\u0000 for all \u0000$ zin mathbb {D} $\u0000 . If \u0000$ fin mathcal {B} $\u0000 of the form \u0000$ f(z)=sum _{n=0}^{infty }a_nz^n $\u0000 , then \u0000$ sum _{n=0}^{infty }|a_nz^n|leq 1 $\u0000 for \u0000$ |z|=rleq 1/3 $\u0000 and \u0000$ 1/3 $\u0000 cannot be improved. This inequality is called Bohr inequality and the quantity \u0000$ 1/3 $\u0000 is called Bohr radius. If \u0000$ fin mathcal {B} $\u0000 of the form \u0000$ f(z)=sum _{n=0}^{infty }a_nz^n $\u0000 , then \u0000$ |sum _{n=0}^{N}a_nz^n|<1;; mbox {for};; |z|<{1}/{2} $\u0000 and the radius \u0000$ 1/2 $\u0000 is the best possible for the class \u0000$ mathcal {B} $\u0000 . This inequality is called Bohr–Rogosinski inequality and the corresponding radius is called Bohr–Rogosinski radius. Let \u0000$ mathcal {H} $\u0000 be the class of all complex-valued harmonic functions \u0000$ f=h+bar {g} $\u0000 defined on the unit disk \u0000$ mathbb {D} $\u0000 , where \u0000$ h $\u0000 and \u0000$ g $\u0000 are analytic in \u0000$ mathbb {D} $\u0000 with the normalization \u0000$ h(0)=h^{prime }(0)-1=0 $\u0000 and \u0000$ g(0)=0 $\u0000 . Let \u0000$ mathcal {H}_0={f=h+bar {g}in mathcal {H} : g^{prime }(0)=0}. $\u0000 For \u0000$ alpha geq 0 $\u0000 and \u0000$ 0leq beta <1 $\u0000 , let \u0000$$ begin{align*} mathcal{W}^{0}_{mathcal{H}}(alpha, beta)={f=h+overline{g}inmathcal{H}_{0} : mathrm{Re}left(h^{prime}(z)+alpha zh^{primeprime}(z)-betaright)>|g^{prime}(z)+alpha zg^{primeprime}(z)|,;; zinmathbb{D}} end{align*} $$\u0000 be a class of close-to-convex harmonic mappings in \u0000$ mathbb {D} $\u0000 . In this paper, we prove the sharp Bohr–Rogosinski radius for the class \u0000$ mathcal {W}^{0}_{mathcal {H}}(alpha , beta ) $\u0000 .","PeriodicalId":55280,"journal":{"name":"Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135306205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali Ebrahimzadeh Esfahani, M. Nemati, Mohammad Reza Ghanei
{"title":"Invariant means on weakly almost periodic functionals with application to quantum groups","authors":"Ali Ebrahimzadeh Esfahani, M. Nemati, Mohammad Reza Ghanei","doi":"10.4153/S0008439523000061","DOIUrl":"https://doi.org/10.4153/S0008439523000061","url":null,"abstract":"Abstract Let \u0000${mathcal A}$\u0000 be a Banach algebra, and let \u0000$varphi $\u0000 be a nonzero character on \u0000${mathcal A}$\u0000 . For a closed ideal I of \u0000${mathcal A}$\u0000 with \u0000$Inot subseteq ker varphi $\u0000 such that I has a bounded approximate identity, we show that \u0000$operatorname {WAP}(mathcal {A})$\u0000 , the space of weakly almost periodic functionals on \u0000${mathcal A}$\u0000 , admits a right (left) invariant \u0000$varphi $\u0000 -mean if and only if \u0000$operatorname {WAP}(I)$\u0000 admits a right (left) invariant \u0000$varphi |_I$\u0000 -mean. This generalizes a result due to Neufang for the group algebra \u0000$L^1(G)$\u0000 as an ideal in the measure algebra \u0000$M(G)$\u0000 , for a locally compact group G. Then we apply this result to the quantum group algebra \u0000$L^1({mathbb G})$\u0000 of a locally compact quantum group \u0000${mathbb G}$\u0000 . Finally, we study the existence of left and right invariant \u0000$1$\u0000 -means on \u0000$ operatorname {WAP}(mathcal {T}_{triangleright }({mathbb G}))$\u0000 .","PeriodicalId":55280,"journal":{"name":"Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques","volume":null,"pages":null},"PeriodicalIF":0.6,"publicationDate":"2023-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44999520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A note on cyclic vectors in Dirichlet-type spaces in the unit ball of \u0000${mathbb C}^n$","authors":"Dimitrios Vavitsas","doi":"10.4153/S0008439523000085","DOIUrl":"https://doi.org/10.4153/S0008439523000085","url":null,"abstract":"Abstract We characterize model polynomials that are cyclic in Dirichlet-type spaces in the unit ball of \u0000$mathbb C^n$\u0000 , and we give a sufficient capacity condition in order to identify noncyclic vectors.","PeriodicalId":55280,"journal":{"name":"Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques","volume":null,"pages":null},"PeriodicalIF":0.6,"publicationDate":"2023-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46821753","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}