Maximal ideal space of some Banach algebras of Dirichlet series
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arXiv
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| Natura: | Preprint |
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2025
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| _version_ | 1866913736338440192 |
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| author | Sasane, Amol |
| author_facet | Sasane, Amol |
| contents | Let $\mathscr{H}^\infty$ be the set of all Dirichlet series $f=\sum\limits_{n=1}^\infty \frac{a_n}{n^s}$ (where $a_n\in \mathbb{C}$ for each $n$) that converge at each $s\in {\mathbb{C}}_+$, such that $\|f\|_{\infty}:=\sup_{s\in {\mathbb{C}}_+}|f(s)|<\infty$. Let $\mathscr{B}\subset \mathscr{H}^\infty$ be a Banach algebra containing the Dirichlet polynomials (Dirichlet series with finitely many nonzero terms) with a norm $\|\cdot\|_{\mathscr{B}}$ such that the inclusion $\mathscr{B} \subset \mathscr{H}^\infty$ is continuous. For $m\in \mathbb{N}=\{1,2,3,\cdots\}$, let $\partial^{-m}\mathscr{B}$ denote the Banach algebra consisting of all $f\in \mathscr{B}$ such that $f',\cdots, f^{(m)}\in \mathscr{B}$, with pointwise operations and the norm $\|f\|_{\partial^{-m}\mathscr{B}}=\sum_{\ell=0}^m \frac{1}{\ell!}\|f^{(\ell)}\|_{\mathscr{B}}$. Assuming that the Wiener $1/f$ property holds for $\mathscr{B}$ (that is, $\inf_{s\in {\mathbb{C}}_+} |f(s)|>0$ implies $\frac{1}{f}\in \mathscr{B}$), it is shown that for all $m\in \mathbb{N}$, the maximal ideal space $M(\partial^{-m}\mathscr{B})$ of $\partial^{-m}\mathscr{B}$ is homeomorphic to $\overline{\mathbb{D}}^{\mathbb{N}}$, where $\overline{\mathbb{D}}=\{z\in \mathbb{C}:|z|\le 1\}$. Examples of such Banach algebras are $\mathscr{H}^\infty$, the subalgebra $\mathscr{A}_u$ of $\mathscr{H}^\infty$ consisting of uniformly continuous functions in ${\mathbb{C}}_+$, and the Wiener algebra $\mathscr{W}$ of Dirichlet series with $\|f\|_{\mathscr{W}}:=\sum_{n=1}^\infty |a_n|<\infty$. Some consequences (existence of logarithms, projective freeness, infinite Bass stable rank) are given as applications. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_11592 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Maximal ideal space of some Banach algebras of Dirichlet series Sasane, Amol Functional Analysis Commutative Algebra Complex Variables Rings and Algebras Primary 30B50, Secondary 46J15, 46E25, 30H05 Let $\mathscr{H}^\infty$ be the set of all Dirichlet series $f=\sum\limits_{n=1}^\infty \frac{a_n}{n^s}$ (where $a_n\in \mathbb{C}$ for each $n$) that converge at each $s\in {\mathbb{C}}_+$, such that $\|f\|_{\infty}:=\sup_{s\in {\mathbb{C}}_+}|f(s)|<\infty$. Let $\mathscr{B}\subset \mathscr{H}^\infty$ be a Banach algebra containing the Dirichlet polynomials (Dirichlet series with finitely many nonzero terms) with a norm $\|\cdot\|_{\mathscr{B}}$ such that the inclusion $\mathscr{B} \subset \mathscr{H}^\infty$ is continuous. For $m\in \mathbb{N}=\{1,2,3,\cdots\}$, let $\partial^{-m}\mathscr{B}$ denote the Banach algebra consisting of all $f\in \mathscr{B}$ such that $f',\cdots, f^{(m)}\in \mathscr{B}$, with pointwise operations and the norm $\|f\|_{\partial^{-m}\mathscr{B}}=\sum_{\ell=0}^m \frac{1}{\ell!}\|f^{(\ell)}\|_{\mathscr{B}}$. Assuming that the Wiener $1/f$ property holds for $\mathscr{B}$ (that is, $\inf_{s\in {\mathbb{C}}_+} |f(s)|>0$ implies $\frac{1}{f}\in \mathscr{B}$), it is shown that for all $m\in \mathbb{N}$, the maximal ideal space $M(\partial^{-m}\mathscr{B})$ of $\partial^{-m}\mathscr{B}$ is homeomorphic to $\overline{\mathbb{D}}^{\mathbb{N}}$, where $\overline{\mathbb{D}}=\{z\in \mathbb{C}:|z|\le 1\}$. Examples of such Banach algebras are $\mathscr{H}^\infty$, the subalgebra $\mathscr{A}_u$ of $\mathscr{H}^\infty$ consisting of uniformly continuous functions in ${\mathbb{C}}_+$, and the Wiener algebra $\mathscr{W}$ of Dirichlet series with $\|f\|_{\mathscr{W}}:=\sum_{n=1}^\infty |a_n|<\infty$. Some consequences (existence of logarithms, projective freeness, infinite Bass stable rank) are given as applications. |
| title | Maximal ideal space of some Banach algebras of Dirichlet series |
| topic | Functional Analysis Commutative Algebra Complex Variables Rings and Algebras Primary 30B50, Secondary 46J15, 46E25, 30H05 |
| url | https://arxiv.org/abs/2503.11592 |