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A resonance phenomenon for ground states of an elliptic equation of Emden–Fowler type. (English) Zbl 1055.34031
The author studies the existence of radial solutions of the elliptic equation \[ \Delta u+u^p+u^q=0\tag{1} \] in \(\mathbb R^N\), \(N\geq 3\), with \(0<u(x)\to+\infty\) as \(| x| \to+\infty\). By C. S. Lin and W. M. Ni [Proc. Am. Math. Soc. 102, 271–277 (1988; Zbl 0652.35085)] it was proved that if \(1<p<\frac{N+2}{N-2}<q\) and \(q=2p-1\), then there exists an explicit radial solution of the form \(u(r)=(\frac{A}{B+r^2})^{\frac{1}{p-1}}\).
In the present paper, this result is generalized. It is proved that if the range of \(p\) is further restricted to \(p>\frac{N+2\sqrt{N-1}}{N+2\sqrt{N-1}-4}\), then for \(q=2p-1\), equation (1) has infinitely many radial solutions with fast decay \(O(r^{2-N})\) besides the explicit solution. If \(q\) is close to \(2p-1\), then equation (1) also has a large number of such solutions.
It is known that the existence of positive radial solutions of (1) is equivalent to the existence of solutions of the ordinary differential equation \[ u''+\frac{N-1}{r}u'+u_+^p+u_+^q=0 \] with \(u'(0)=0\), \(0<u(r)\to+\infty\) where \(u_+=\max\{u, 0\}\). This equation can be further reduced to the second-order differential equation \[ x''-\alpha x'+x_+^p+e^{-\gamma t}x_+^q-\beta x=0 \] by using the classical transformation \(x(t)=r^{\frac{2}{p-1}}u(r)| _{r=e^t}\). On the basis of this preparation, the invariant manifold theory is used to prove the existence of solutions \(x(t)\) satisfying \(x(t)\to 0\) as \(t\to\pm\infty\).

34B15 Nonlinear boundary value problems for ordinary differential equations
35J60 Nonlinear elliptic equations
35B34 Resonance in context of PDEs
34D05 Asymptotic properties of solutions to ordinary differential equations
34C45 Invariant manifolds for ordinary differential equations
Full Text: DOI
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