An improved Hardy-Trudinger-Moser inequality

Abstract

Let $\mathbb{B}$ be the unit disc in $\mathbb{R}^2$, $\mathscr{H}$ be the completion of $C_0^\infty(\mathbb{B})$ under the norm $$\|u\|_{\mathscr{H}}=\left(\int_\mathbb{B}|\nabla u|^2dx-\int_\mathbb{B}\frac{u^2}{(1-|x|^2)^2}dx\right)^{1/2},\quad\forall u\in C_0^\infty(\mathbb{B}).$$ Denote $\lambda_1(\mathbb{B})=\inf_{u\in \mathscr{H},\,\|u\|_2=1}\|u\|_{\mathscr{H}}^2$, where $\|\cdot\|_2$ stands for the $L^2(\mathbb{B})$-norm. Using blow-up analysis, we prove that for any $\alpha$, $0\leq \alpha<\lambda_1(\mathbb{B})$, $$\sup_{u\in\mathscr{H},\,\|u\|_{\mathscr{H}}^2-\alpha\|u\|_2^2\leq 1}\int_\mathbb{B} e^{4\pi u^2}dx<+\infty,$$ and that the above supremum can be attained by some function $u\in \mathscr{H}$ with $\|u\|_{\mathscr{H}}^2-\alpha\|u\|_2^2= 1$. This improves an earlier result of G. Wang and D. Ye [28].