Resolvent, spectrum and resonances for the acoustic operator with piecewise constant coefficients
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866912845744046080 |
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| author | Mantile, Andrea Posilicano, Andrea |
| author_facet | Mantile, Andrea Posilicano, Andrea |
| contents | We study the acoustic operator $A_{v,ρ}:=v^{2}ρ\nabla\!\cdotρ^{-1}\nabla$ with transmission conditions at the boundary of $Ω=Ω_{1}\cup\dots\cupΩ_{n}$, where the $Ω_{\ell}$'s are connected disjoint open bounded Lipschitz domains, the positive functions $v$ and $ρ$ are constant on each connected component of $Ω$ and $v=ρ=1$ on ${\mathbb R}^{3}\backslash\overlineΩ$. Through a formula for the resolvents difference $(-A_{v,ρ}+z)^{-1}-(-Δ+z)^{-1}$, we provide a Limiting Absorption Principle, determine the spectrum, which turns out to be purely absolutely continuous, and, in the case the connected components of $Ω$ are of class ${\mathcal C}^{1,α}$, characterize the resonance set. The second part of the paper is devoted to the case where $Ω=Ω(\varepsilon)$ is connected with a small size $\varepsilon$ and the $\varepsilon$-analytic functions $v=v(\varepsilon)$ and/or $ρ=ρ(\varepsilon)$ converge to $0_{+}$ inside $Ω(\varepsilon)$ as $\varepsilon\downarrow 0$; there, we provide the analytic $\varepsilon$-expansions of the resonances of $A_{v,ρ}$ according to different choices of the rate of convergence towards zero of the material parameters. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_17522 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Resolvent, spectrum and resonances for the acoustic operator with piecewise constant coefficients Mantile, Andrea Posilicano, Andrea Analysis of PDEs Mathematical Physics Spectral Theory We study the acoustic operator $A_{v,ρ}:=v^{2}ρ\nabla\!\cdotρ^{-1}\nabla$ with transmission conditions at the boundary of $Ω=Ω_{1}\cup\dots\cupΩ_{n}$, where the $Ω_{\ell}$'s are connected disjoint open bounded Lipschitz domains, the positive functions $v$ and $ρ$ are constant on each connected component of $Ω$ and $v=ρ=1$ on ${\mathbb R}^{3}\backslash\overlineΩ$. Through a formula for the resolvents difference $(-A_{v,ρ}+z)^{-1}-(-Δ+z)^{-1}$, we provide a Limiting Absorption Principle, determine the spectrum, which turns out to be purely absolutely continuous, and, in the case the connected components of $Ω$ are of class ${\mathcal C}^{1,α}$, characterize the resonance set. The second part of the paper is devoted to the case where $Ω=Ω(\varepsilon)$ is connected with a small size $\varepsilon$ and the $\varepsilon$-analytic functions $v=v(\varepsilon)$ and/or $ρ=ρ(\varepsilon)$ converge to $0_{+}$ inside $Ω(\varepsilon)$ as $\varepsilon\downarrow 0$; there, we provide the analytic $\varepsilon$-expansions of the resonances of $A_{v,ρ}$ according to different choices of the rate of convergence towards zero of the material parameters. |
| title | Resolvent, spectrum and resonances for the acoustic operator with piecewise constant coefficients |
| topic | Analysis of PDEs Mathematical Physics Spectral Theory |
| url | https://arxiv.org/abs/2601.17522 |