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The Fourier extension operator of distributions in Sobolev spaces of the sphere and the Helmholtz equation

Published online by Cambridge University Press:  16 November 2020

J. A. Barceló
Affiliation:
Departamento de Matemática e Informática aplicadas a las Ingenierías Civil y Naval, Universidad Politécnica de Madrid, Madrid, 28040, Spain ([email protected])
M. Folch-Gabayet
Affiliation:
Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, 04510, México ([email protected])
T. Luque
Affiliation:
Departamento de Análisis Matemático y Matemática Aplicada, Universidad Complutense de Madrid, Madrid, 28040, Spain ([email protected])
S. Pérez-Esteva
Affiliation:
Instituto de Matemáticas, Unidad de Cuernavaca, Universidad Nacional Autónoma de México, México ([email protected])
M. C. Vilela
Affiliation:
ETSI Navales, Departamento de Matemática e Informática aplicadas a las Ingenierías Civil y Naval, Universidad Politécnica de Madrid, Madrid, 28040, Spain ([email protected])

Abstract

The purpose of this paper is to characterize the entire solutions of the homogeneous Helmholtz equation (solutions in ℝd) arising from the Fourier extension operator of distributions in Sobolev spaces of the sphere $H^\alpha (\mathbb {S}^{d-1}),$ with α ∈ ℝ. We present two characterizations. The first one is written in terms of certain L2-weighted norms involving real powers of the spherical Laplacian. The second one is in the spirit of the classical description of the Herglotz wave functions given by P. Hartman and C. Wilcox. For α > 0 this characterization involves a multivariable square function evaluated in a vector of entire solutions of the Helmholtz equation, while for α < 0 it is written in terms of an spherical integral operator acting as a fractional integration operator. Finally, we also characterize all the solutions that are the Fourier extension operator of distributions in the sphere.

Type
Research Article
Copyright
Copyright © The Author(s), 2020. Published by Cambridge University Press on behalf of The Royal Society of Edinburgh

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