Some weighted fourth-order Hardy-Henon equations
By using a suitable transform related to Sobolev inequality, we investigate the sharp constants and optimizers in radial space for the following weighted Caffarelli-Kohn-Nirenberg-type inequalities: \begin{equation*} \int_{\mathbb{R}^N}|x|^α|Δu|^2 dx \geq S^{rad}(N,α)\left(\int_{\mathbb{R}^N}|x|^{-α}|u|^{p^*_α} dx\right)^{\frac{2}{p^*_α}}, \quad u\in C^\infty_c(\mathbb{R}^N), \end{equation*} where $N\geq 3$, $4-N<α<2$, $p^*_α=\frac{2(N-α)}{N-4+α}$. Then we obtain the explicit form of the unique (up to scaling) radial positive solution $U_{λ,α}$ to the weighted fourth-order Hardy (for $α>0$) or Hénon (for $α<0$) equation: \begin{equation*} Δ(|x|^αΔu)=|x|^{-α} u^{p^*_α-1},\quad u>0 \quad \mbox{in}\quad \mathbb{R}^N. \end{equation*} %Furthermore, we characterize all the solutions to the linearized problem related to above equation at $U_{1,α}$. For $α\neq 0$, it is known the solutions of above equation are invariant for dilations $λ^{\frac{N-4+α}{2}}u(λx)$ but not for translations. However we show that if $α$ is an even integer, there exist new solutions to the linearized problem, which related to above equation at $U_{1,α}$, that "replace" the ones due to the translations invariance. This interesting phenomenon was first shown by Gladiali, Grossi and Neves [Adv. Math. 249, 2013, 1-36] for the second-order Hénon problem. Finally, as applications, we investigate the reminder term of above inequality and also the existence of solutions to some related perturbed equations.