Mountain pass solutions and an indefinite superlinear elliptic problem on $\mathbb R^{\mathbb N}$

Yihong Du, Yuxia Guo



We consider the elliptic problem
-\Delta u-\lambda u=a(x) g(u),
with $a(x)$ sign-changing and $g(u)$ behaving like $u^p$, $p> 1$.
Under suitable conditions on $g(u)$ and $a(x)$, we extend the
multiplicity, existence and nonexistence results known to hold for
this equation on a bounded domain (with standard homogeneous
boundary conditions) to the case that the bounded domain is
replaced by the entire space $\mathbb R^N$. More precisely, we show that
there exists $\Lambda> 0$ such that this equation on $\mathbb R^N$ has no
positive solution for $\lambda> \Lambda$, at least two positive
solutions for $\lambda\in (0,\Lambda)$, and at least one positive
solution for $\lambda\in (-\infty,0]\cup\{\Lambda\}$.

Our approach is based on some descriptions of mountain pass
solutions of semilinear elliptic problems on bounded domains
obtained by a special version of the mountain pass theorem. These
results are of independent interests.


Mountain pass solution; Morse index; a priori estimates

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