# Paley-Wiener theorem

A function vanishes almost everywhere outside an interval if and only if its Fourier transform

satisfies

and is the restriction to the real line of a certain entire analytic function of a complex variable satisfying for all (see [1]). A description of the image of a certain space of functions or generalized functions on a locally compact group under the Fourier transform or under some other injective integral transform is called an analogue of the Paley–Wiener theorem; the most frequently encountered analogues of the Paley–Wiener theorem are a description of the image of the space of infinitely-differentiable functions of compact support and a description of the image of the space of rapidly-decreasing infinitely-differentiable functions on a locally compact group under the Fourier transform on . Such analogues are known, in particular, for Abelian locally compact groups, for certain connected Lie groups, for certain subalgebras of the algebra on real semi-simple Lie groups, and also for certain other integral transforms.

#### References

[1] | N. Wiener, R.E.A.C. Paley, "Fourier transforms in the complex domain" , Amer. Math. Soc. (1934) |

[2] | V.S. Vladimirov, "Generalized functions in mathematical physics" , MIR (1977) (Translated from Russian) |

[3] | I.M. Gel'fand, M.I. Graev, N.Ya. Vilenkin, "Generalized functions" , 5. Integral geometry and representation theory , Acad. Press (1966) (Translated from Russian) |

[4] | D.P. Zhelobenko, "Harmonic analysis of functions on semi-simple complex Lie groups" , Moscow (1974) (In Russian) |

[5] | W. Rudin, "Functional analysis" , McGraw-Hill (1973) |

#### Comments

Let with . Then the Fourier transform of can be extended to an entire analytic function on satisfying: for any integer there is a constant such that for all ,

(*) |

Conversely, let be an entire function which satisfies (*) (replacing with ), for some . Then there exists a with and .

#### References

[a1] | F. Trèves, "Topological vectorspaces, distributions and kernels" , Acad. Press (1967) |

[a2] | G. Warner, "Harmonic analysis on semi-simple Lie groups" , II , Springer (1972) |

[a3] | S. Helgason, "Groups and geometric analysis" , Acad. Press (1984) pp. Chapt. II, Sect. 4 |

[a4] | Y. Katznelson, "An introduction to harmonic analysis" , Dover, reprint (1976) |

**How to Cite This Entry:**

Paley-Wiener theorem.

*Encyclopedia of Mathematics.*URL: http://www.encyclopediaofmath.org/index.php?title=Paley-Wiener_theorem&oldid=22883