Dirichlet-type energy of mappings between two concentric annuli

TL;DR

This paper investigates the minimizers of a Dirichlet-type energy for mappings between spherical annuli, confirming a conjecture that such minimizers are generalized radial diffeomorphisms for dimensions four and higher.

Contribution

It generalizes previous results by analyzing a combined energy integral and supports the conjecture that minimizers are generalized radial diffeomorphisms in higher dimensions.

Findings

Minimizers of the combined energy integral are generalized radial diffeomorphisms.

For dimensions n ≥ 4, actual minimizers of the energy do not exist, but minimizing sequences do.

The results extend previous work on the case n=3 to higher dimensions.

Abstract

Let $\mathbb{A}$ and $\mathbb{A_{*}}$ be two non-degenerate spherical annuli in $\mathbb{R}^{n}$ equipped with the Euclidean metric and the weighted metric $|y|^{1-n}$, respectively. Let $\mathcal{F}(\mathbb{A},\mathbb{A_{*}})$ denote the class of homeomorphisms in $\mathcal{W}^{1,n-1}(\mathbb{A},\mathbb{A_{*}})$. For $n=3$, the second author \cite{kalaj2018} proved that the minimizers of the Dirichlet-type energy $\mathcal{E}[h]=\int_{\mathbb{A}} \frac{\|Dh(x)\|^{n-1}}{|h(x)|^{n-1}}dx$ are certain generalized radial diffeomorphisms, where $h\in \mathcal{F}(\mathbb{A},\mathbb{A_{*}})$. For the case $n\geq 4$, he conjectured that the minimizers are also certain generalized radial diffeomorphisms between $\mathbb{A}$ and $\mathbb{A_{*}}$. The main aim of this paper is to consider this conjecture. First, we investigate the minimality of the following combined energy integral: $$ \mathbb{E}[a,b][h] =\int_{\mathbb{A}}\frac{a^{2}\rho^{n-1}(x)\|DS(x)\|^{n-1}+b^{2}|\nabla \rho(x)|^{n-1}}{|\rho(x)|^{n-1}}dx, $$ where $h=\rho S\in \mathcal{F}(\mathbb{A},\mathbb{A_{*}})$, $\rho=|h|$ and $a,b>0$. The obtained result is a generalization of \cite[Theorem 1.1]{kalaj2018}. As an application, we show that the above conjecture is almost true for the case $n\geq 4$, i.e., the minimizer of the energy integral $\mathcal{E}[h]$ does not exist but there exists a minimizing sequence which belongs to the generalized radial mappings.