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Topological divisors of zero and Shilov boundary

Authors: Escassut, Alain;

Topological divisors of zero and Shilov boundary

Abstract

Let \(L\) be a non-archimedean and non-trivially complete valued field, let \((A, \|. \| )\) be a commutative normed \(L\)-algebra with unity, and let \(\|.\| _{si}\) be the spectral seminorm of \(A\) defined by \(\| x \| _{si}:= \lim_{n} \| x^n \| ^{1/n}\). The Shilov boundary of \(A\) is the smallest among all the subsets \(F\) of Mult\((A,\|. \| _{si})\) (the set of all non-zero multiplicative \(\| . \| _{si}\)-continuous seminorms on \(A\)) that satisfy the following properties: (a) \(F\) is closed (with respect to the topology of simple convergence on \(\text{Mult}(A,\|.\| _{si})\)); (b) for each \(x \in A\) there exists a \(\psi \in F\) such that \(\psi(x) = \| x \| _{si}\). Also, an \(f \in A\) is said to be a topological divisor of zero if there exists a sequence \((x_n)_n\) in \(A\) such that \(\inf_n \| x_n \| >0\) and \(\lim_{n} \| f x_n \| =0\)). The author gives the following description for the topological divisors of zero by means of the Shilov boundary: If \(\|.\| = \|.\| _{si}\), then an \(f \in A\) is a topological divisor of zero if and only if there exists a \(\psi\) in the Shilov boundary of \(A\) such that \(\psi(f) =0\). He also proves that if \(A\) is a Banach \(L\)-algebra and if \(f \in A\) is not a divisor of zero, then \(f\) is a topological divisor of zero if and only if the ideal \(f A\) is not closed. By using these results, together with other ones obtained by the author in some of his previous papers, he derives interesting properties for the topological divisors of zero of certain types of algebras. Among them, we point out the following : (1) Let \(A\) be a Noetherian Banach \(L\)-algebra (e.g., \(A\) is an \(L\)-affinoid algebra\()\). Then any topological divisor of zero is a divisor of zero. (2) Let \(K\) be a complete algebraically closed field extension of \(L\), let \(D\) be a closed bounded infraconnected subset of \(K\), let \(H(D)\) be the completion of the \(K\)-algebra of rational functions without poles in \(D\), equipped with the norm of uniform convergence on \(D\). Then, for an \(f \in H(D)\), \(f \neq 0\), the following are equivalent: \((\alpha)\) \(f\) is a topological divisor of zero, \((\beta)\) the ideal \(f H(D)\) is not closed, \((\gamma)\) \(f\) is not quasi-invertible (i.e., it does not admit a factorization in the form \(Pg\) where \(g\) is an invertible element of \(H(D)\) and \(P\) is a polynomial whose zeros lie in the interior of \(D\)).

Keywords

Topological divisors of zero, topological divisors of zero, Ultrametric algebras, Multiplicative semi-norms, Non-Archimedean valued fields, Functional analysis over fields other than \(\mathbb{R}\) or \(\mathbb{C}\) or the quaternions; non-Archimedean functional analysis, multiplicative semi-norms, Geometry and Topology, Shilov boundary, ultrametric algebras, [MATH.MATH-NT] Mathematics [math]/Number Theory [math.NT]

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
4
Average
Average
Average
hybrid