Least energy solutions for an elliptic problem involving sublinear term and peaking phenomenon
Qiuping Lu  School of Mathematical Science, Yangzhou University, Yangzhou 225002, China, China (email) Abstract: For a general elliptic problem $\triangle{u} = g(u)$ in $R^N$ with $N \ge 3$, we show that all solutions have compact support and there exists a least energy solution, which is radially symmetric and decreases with respect to $x = r$. With this result we study a singularly perturbed elliptic problem $ \epsilon^{2} \triangle{u} + u^{q1}u = \lambda u + f(u)$ in a bounded domain $\Omega$ with $0 < q < 1 $, $\lambda \ge 0$ and $ u \in H^1_0(\Omega) $. For any $y \in \Omega$, we show that there exists a least energy solution $u_{\epsilon}$, which concentrates around this point $y$ as $\epsilon \to 0$. Conversely when $\epsilon $ is small, the boundary of the set $\{ x \in \Omega  u_{\epsilon}(x)>0 \}$ is a free boundary, where $u_{\epsilon}$ is any nonnegative least energy solution.
Keywords: Semilinear elliptic equation, least energy solution, sublinear, singular perturbation.
Received: March 2015; Revised: July 2015; Available Online: September 2015. 
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