Electron. J. Differential Equations, Vol. 2025 (2025), No. 86, pp. 1-21.

Existence and multiplicity of solutions to triharmonic problems

Qifan Wei, Xuemei Zhang

Abstract:
The authors consider the triharmonic equation $$ (-\Delta)^3u+c_1\Delta^2 u+c_2\Delta u=h(x)|u|^{p-2} u+g(x,u) $$ in \(\Omega\), where \(p\in(1,2)\), subject to Navier boundary conditions. Based on the least action principle, the Ekeland's variational principle and a variant version of mountain pass lemma, we analyze the existence and multiplicity of nontrivial solutions to the above problem. In addition, we obtain the first eigenvalue of triharmonic operator and consider its structure. The conclusions are illustrated with several examples.

Submitted June 23, 2025. Published August 18, 2025.
Math Subject Classifications: 35J30, 35J40.
Key Words: Triharmonic equation; Ekeland's variational principle; mountain pass lemma; existence and multiplicity of solutions
DOI: 10.58997/ejde.2025.86

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Qifan Wei
School of Mathematics and Physics
North China Electric Power University
Beijing 102206, China
email: weiqifan0924@163.com
Xuemei Zhang
School of Mathematics and Physics
North China Electric Power University
Beijing 102206, China
email: zxm74@sina.com

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