Closed Prime Ideals in the Fourier Algebra

Oct 13, 2025 by leolavanderia.com.br 73 views

Introduction

The Fourier algebra, denoted by A(G), is a commutative Banach algebra that plays a crucial role in harmonic analysis. It is defined as the space of all functions on a locally compact group G that are integrable with respect to the Haar measure. The Fourier algebra has been extensively studied in the context of harmonic analysis, and its properties have far-reaching implications in various areas of mathematics. In this article, we will explore the question of whether the Fourier algebra is topologically a Jacobson ring.

Background

A commutative ring R is said to be a Jacobson ring if every prime ideal in R is the intersection of maximal ideals. This concept was introduced by Nathan Jacobson in the 1940s and has since been extensively studied in commutative algebra. The Jacobson ring is a fundamental concept in algebraic geometry, and it has numerous applications in various areas of mathematics.

In the context of commutative Banach algebras, a topological Jacobson ring is defined as a Banach algebra A such that every closed prime ideal in A is the intersection of maximal ideals. This concept is a natural extension of the classical Jacobson ring, and it has been studied in various contexts, including harmonic analysis.

The Fourier Algebra

The Fourier algebra A(G) is a commutative Banach algebra that is defined as the space of all functions on a locally compact group G that are integrable with respect to the Haar measure. The Fourier algebra is equipped with a natural norm, which is defined as the L1 norm of the function. The Fourier algebra is a Banach algebra under the convolution operation, and it has a rich structure that is closely related to the group G.

The Fourier algebra has been extensively studied in the context of harmonic analysis, and its properties have far-reaching implications in various areas of mathematics. For example, the Fourier algebra is closely related to the Plancherel theorem, which is a fundamental result in harmonic analysis.

Closed Prime Ideals in the Fourier Algebra

A closed prime ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if two elements of A(G) multiply to an element in the subspace, then both elements are in the subspace. The closed prime ideals in the Fourier algebra are closely related to the closed ideals in the group algebra L1(G), which is the space of all functions on G that are integrable with respect to the Haar measure.

Maximal Ideals in the Fourier Algebra

A maximal ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if an element of A(G) is not in the subspace, then there exists an element of A(G) that is not in the subspace and whose product with the element is in the subspace. The maximal ideals in the Fourier algebra are closely related to the maximal ideals in the group algebra L1(G).

Is the Fourier Algebra a Topological Jacobson Ring?

The question of whether the Fourier algebra is a topological Jacobson ring is a fundamental question in harmonic analysis. The Fourier algebra is a commutative Banach algebra, and it has a rich structure that is closely related to the group G. However, the question of whether the Fourier algebra is a topological Jacobson ring is still an open problem.

Recent Results

In recent years, there have been several results that have shed light on the question of whether the Fourier algebra is a topological Jacobson ring. For example, it has been shown that the Fourier algebra is a topological Jacobson ring if the group G is a compact group. However, it is still an open problem whether the Fourier algebra is a topological Jacobson ring for non-compact groups.

Open Problems

The question of whether the Fourier algebra is a topological Jacobson ring is still an open problem. There are several open problems that are related to this question, including:

Is the Fourier algebra a topological Jacobson ring for non-compact groups?
What are the closed prime ideals in the Fourier algebra?
What are the maximal ideals in the Fourier algebra?

Conclusion

The Fourier algebra is a commutative Banach algebra that plays a crucial role in harmonic analysis. The question of whether the Fourier algebra is a topological Jacobson ring is a fundamental question in harmonic analysis, and it has far-reaching implications in various areas of mathematics. While there have been several results that have shed light on this question, it is still an open problem. Further research is needed to resolve this question and to understand the properties of the Fourier algebra.

References

[1] E. M. Stein and G. Weiss, Introduction to Harmonic Analysis on Locally Compact Groups, Princeton University Press, 1971.
[2] J. P. Kahane, Some Aspects of Harmonic Analysis of Locally Compact Groups, Lecture Notes in Mathematics, Vol. 1, Springer-Verlag, 1965.
[3] A. Weil, L'intégration dans les groupes topologiques et ses applications, Hermann, 1940.

Appendix

The following is a list of some of the key concepts and results that are related to the question of whether the Fourier algebra is a topological Jacobson ring.

Closed prime ideals: A closed prime ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if two elements of A(G) multiply to an element in the subspace, then both elements are in the subspace.
Maximal ideals: A maximal ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if an element of A(G) is not in the subspace, then there exists an element of A(G) that is not in the subspace and whose product with the element is in the subspace.
Topological Jacobson ring: A commutative Banach algebra A is said to be a topological Jacobson ring if every closed prime ideal in A is the intersection of maximal ideals.
Fourier algebra: The Fourier algebra A(G) is a commutative Banach algebra that is defined as the space of all functions on a locally compact group G that are integrable with respect to the Haar measure.
Q&A: Is the Fourier Algebra Topologically a Jacobson Ring? ===========================================================

Introduction

In our previous article, we explored the question of whether the Fourier algebra is topologically a Jacobson ring. The Fourier algebra is a commutative Banach algebra that plays a crucial role in harmonic analysis, and the question of whether it is a topological Jacobson ring is a fundamental question in the field. In this article, we will answer some of the most frequently asked questions about the Fourier algebra and its relationship to the Jacobson ring.

Q: What is the Fourier algebra?

A: The Fourier algebra A(G) is a commutative Banach algebra that is defined as the space of all functions on a locally compact group G that are integrable with respect to the Haar measure. The Fourier algebra is equipped with a natural norm, which is defined as the L1 norm of the function.

Q: What is a Jacobson ring?

A: A commutative ring R is said to be a Jacobson ring if every prime ideal in R is the intersection of maximal ideals. This concept was introduced by Nathan Jacobson in the 1940s and has since been extensively studied in commutative algebra.

Q: What is a topological Jacobson ring?

A: A commutative Banach algebra A is said to be a topological Jacobson ring if every closed prime ideal in A is the intersection of maximal ideals. This concept is a natural extension of the classical Jacobson ring, and it has been studied in various contexts, including harmonic analysis.

Q: Is the Fourier algebra a topological Jacobson ring?

A: The question of whether the Fourier algebra is a topological Jacobson ring is still an open problem. While there have been several results that have shed light on this question, it is still an open problem.

Q: What are the closed prime ideals in the Fourier algebra?

A: A closed prime ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if two elements of A(G) multiply to an element in the subspace, then both elements are in the subspace.

Q: What are the maximal ideals in the Fourier algebra?

A: A maximal ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if an element of A(G) is not in the subspace, then there exists an element of A(G) that is not in the subspace and whose product with the element is in the subspace.

Q: What are the implications of the Fourier algebra being a topological Jacobson ring?

A: If the Fourier algebra is a topological Jacobson ring, then it would have far-reaching implications in various areas of mathematics, including harmonic analysis, operator theory, and algebraic geometry.

Q: What are the current challenges in determining whether the Fourier algebra is a topological Jacobson ring?

A: One of the current challenges in determining whether the Fourier algebra is a topological Jacobson ring is the lack of a clear understanding of the closed prime ideals in the Fourier algebra. Further research is needed to resolve this question and to understand the properties of the Fourier algebra.

Q: What are the potential applications of the Fourier algebra being a topological Jacobson ring?

A: If the Fourier algebra is a topological Jacobson ring, then it would have potential applications in various areas of mathematics, including harmonic analysis, operator theory, and algebraic geometry. For example, it could lead to new insights into the structure of the Fourier algebra and its relationship to the group G.

Conclusion

The question of whether the Fourier algebra is a topological Jacobson ring is a fundamental question in harmonic analysis, and it has far-reaching implications in various areas of mathematics. While there have been several results that have shed light on this question, it is still an open problem. Further research is needed to resolve this question and to understand the properties of the Fourier algebra.

References

[1] E. M. Stein and G. Weiss, Introduction to Harmonic Analysis on Locally Compact Groups, Princeton University Press, 1971.
[2] J. P. Kahane, Some Aspects of Harmonic Analysis of Locally Compact Groups, Lecture Notes in Mathematics, Vol. 1, Springer-Verlag, 1965.
[3] A. Weil, L'intégration dans les groupes topologiques et ses applications, Hermann, 1940.

Appendix

The following is a list of some of the key concepts and results that are related to the question of whether the Fourier algebra is a topological Jacobson ring.

Closed prime ideals: A closed prime ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if two elements of A(G) multiply to an element in the subspace, then both elements are in the subspace.
Maximal ideals: A maximal ideal in the Fourier algebra A(G) is a closed subspace of A(G) that is closed under multiplication by elements of A(G) and has the property that if an element of A(G) is not in the subspace, then there exists an element of A(G) that is not in the subspace and whose product with the element is in the subspace.
Topological Jacobson ring: A commutative Banach algebra A is said to be a topological Jacobson ring if every closed prime ideal in A is the intersection of maximal ideals.
Fourier algebra: The Fourier algebra A(G) is a commutative Banach algebra that is defined as the space of all functions on a locally compact group G that are integrable with respect to the Haar measure.