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A new proof of the Hardy–Rellich inequality in any dimension

Published online by Cambridge University Press:  19 August 2019

Cristian Cazacu*
Affiliation:
Faculty of Mathematics and Computer Science & The Research Institute of the University of Bucharest (ICUB), University of Bucharest, 14 Academiei Street, 010014 Bucharest, Romania ([email protected])

Abstract

The Hardy-Rellich inequality in the whole space with the best constant was firstly proved by Tertikas and Zographopoulos in Adv. Math. (2007) in higher dimensions N ⩾ 5. Then it was extended to lower dimensions N ∈ {3, 4} by Beckner in Forum Math. (2008) and Ghoussoub-Moradifam in Math. Ann. (2011) by applying totally different techniques.

In this note, we refine the method implemented by Tertikas and Zographopoulos, based on spherical harmonics decomposition, to give an easy and compact proof of the optimal Hardy–Rellich inequality in any dimension N ⩾ 3. In addition, we provide minimizing sequences which were not explicitly mentioned in the quoted papers in lower dimensions N ∈ {3, 4}, emphasizing their symmetry breaking. We also show that the best constant is not attained in the proper functional space.

Type
Research Article
Copyright
Copyright © 2019 The Royal Society of Edinburgh

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