Some multiplicity results for a superlinear elliptic problem in $\mathbb R^N$

Abstract

In this paper we shall study the semilinear elliptic problem $$ \begin{cases} -\Delta u +\sigma(x)u= |u|^{p-2}u + f(x) & \text{in }\mathbb R^N,\\ u\rightarrow 0\quad\text{as } |x| \rightarrow\infty, \end{cases} $$ where $\sigma(x) \rightarrow\infty$ as $| x| \rightarrow\infty$, $p> 2$ and $f\in L^{2}(\mathbb R^{N})$. Thanks to a compact embedding of a suitable weigthed Sobolev space in $L^{2}(\mathbb R^{N})$, a direct use of the Symmetric Mountain Pass Theorem (if $f=0$) and of the fibering method (if $f\neq 0$) allows to extend some multiplicity results, already known in the case of bounded domains.