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\begin{document}$$\rho >0$$\end{document}, we study the elliptic problem find(U,λ)∈H01(Ω)×Rsuch that-ΔU+λU=|U|p-1U∫ΩU2dx=ρ,\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} \text {find } (U,\lambda )\in H^1_0(\Omega )\times {\mathbb {R}}\text { such that } {\left\{ \begin{array}{ll} -\Delta U+\lambda U=|U|^{p-1}U\\ \int _{\Omega } U^2\, dx=\rho , \end{array}\right. } \end{aligned}$$\end{document}where Ω⊂RN\documentclass[12pt]{minimal}
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\begin{document}$$\Omega \subset {\mathbb {R}}^N$$\end{document} is a bounded domain and p>1\documentclass[12pt]{minimal}
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\begin{document}$$p>1$$\end{document} is Sobolev-subcritical, searching for conditions (about ρ\documentclass[12pt]{minimal}
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\begin{document}$$\rho $$\end{document}, N and p) for the existence of solutions. By the Gagliardo-Nirenberg inequality it follows that, when p is L2\documentclass[12pt]{minimal}
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\begin{document}$$L^2$$\end{document}-subcritical, i.e. 1<p<1+4/N\documentclass[12pt]{minimal}
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\begin{document}$$1<p<1+4/N$$\end{document}, the problem admits solutions for every ρ>0\documentclass[12pt]{minimal}
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\begin{document}$$\rho >0$$\end{document}. In the L2\documentclass[12pt]{minimal}
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\begin{document}$$L^2$$\end{document}-critical and supercritical case, i.e. when 1+4/N≤p<2∗-1\documentclass[12pt]{minimal}
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\begin{document}$$1+4/N \le p < 2^*-1$$\end{document}, we show that, for any k∈N\documentclass[12pt]{minimal}
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\begin{document}$$k\in {\mathbb {N}}$$\end{document}, the problem admits solutions having Morse index bounded above by k only if ρ\documentclass[12pt]{minimal}
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\begin{document}$$\rho $$\end{document} is sufficiently small. Next we provide existence results for certain ranges of ρ\documentclass[12pt]{minimal}
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\begin{document}$$\rho $$\end{document}, which can be estimated in terms of the Dirichlet eigenvalues of -Δ\documentclass[12pt]{minimal}
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\begin{document}$$-\Delta $$\end{document} in H01(Ω)\documentclass[12pt]{minimal}
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\begin{document}$$H^1_0(\Omega )$$\end{document}, extending to changing sign solutions and to general domains some results obtained in Noris et al. in Anal. PDE 7:1807–1838, 2014 for positive solutions in the ball.