# Critical potentials of the eigenvalues and eigenvalue gaps of Schrödinger operators

Abstract : Let $M$ be a compact Riemannian manifold with or without boundary, and let $-\Delta$ be its Laplace-Beltrami operator. For any bounded scalar potential $q$, we denote by $\lambda_i(q)$ the $i$-th eigenvalue of the Schrödinger type operator $-\Delta + q$ acting on functions with Dirichlet or Neumann boundary conditions in case $\partial M \neq \emptyset$. We investigate critical potentials of the eigenvalues $\lambda_i$ and the eigenvalue gaps $G_{ij}=\lambda_j -\lambda_i$ considered as functionals on the set of bounded potentials having a given mean value on $M$. We give necessary and sufficient conditions for a potential $q$ to be critical or to be a local minimizer or a local maximizer of these functionals. For instance, we prove that a potential $q \in L^\infty (M)$ is critical for the functional $\lambda_2$ if and only if, $q$ is smooth, $\lambda_2( q)=\lambda_3( q)$ and there exist second eigenfunctions $f_1 ,\ldots,f_k$ of $-\Delta + q$ such that $\Sigma_j f_j^2 = 1$. In particular, $\lambda_2$ (as well as any $\lambda_i$) admits no critical potentials under Dirichlet Boundary conditions. Moreover, the functional $\lambda_2$ never admits locally minimizing potentials.
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Journal of Mathematical Analysis and Applications, Elsevier, 2006, 314, pp.195-209
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https://hal.archives-ouvertes.fr/hal-00005320
Contributeur : Ahmad El Soufi <>
Soumis le : vendredi 10 juin 2005 - 18:33:40
Dernière modification le : jeudi 20 décembre 2018 - 01:27:06
Document(s) archivé(s) le : jeudi 1 avril 2010 - 20:23:47

### Citation

Ahmad El Soufi, Nazih Moukadem. Critical potentials of the eigenvalues and eigenvalue gaps of Schrödinger operators. Journal of Mathematical Analysis and Applications, Elsevier, 2006, 314, pp.195-209. 〈hal-00005320〉

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