Arbitrary many positive solutions for a nonlinear problem involving the   fractional Laplacian
  We establish the existence and multiplicity of positive solutions to the problems involving the fractional Laplacian: \begin{equation*} \left\{\begin{array}{lll} &(-\Delta)^{s}u=\lambda u^{p}+f(u),\,\,u>0 \quad &\mbox{in}\,\,\Omega,\\ &u=0\quad &\mbox{in}\,\,\mathbb{R}^{N}\setminus\Omega,\\ \end{array}\right. \end{equation*} where $\Omega\subset \mathbb{R}^{N}$ $(N\geq 2)$ is a bounded smooth domain, $s\in (0,1)$, $p>0$, $\lambda\in \mathbb{R}$ and $(-\Delta)^{s}$ stands for the fractional Laplacian. When $f$ oscillates near the origin or at infinity, via the variational argument we prove that the problem has arbitrarily many positive solutions and the number of solutions to problem is strongly influenced by $u^{p}$ and $\lambda$. Moreover, various properties of the solutions are also described in $L^{\infty}$- and $X^{s}_{0}(\Omega)$-norms. 
Jinguo Zhang, Xiaochun Liu
math.AP