*preprint*

**Inserted:** 17 jul 2018

**Year:** 2016

**Abstract:**

In this paper we perform a blow-up and quantization analysis of the
fractional Liouville equation in dimension $1$. More precisely, given a
sequence $u_k :\mathbb{R} \to \mathbb{R}$ of solutions to \begin{equation}
(-\Delta)^{\frac{1}{2}} u_{k} =K_{ke}^{{u}_{k}\quad} \text{in }\mathbb{R},
\end{equation} with $K_k$ bounded in $L^\infty$ and $e^{u_k}$ bounded in $L^1$
uniformly with respect to $k$, we show that up to extracting a subsequence
$u_k$ can blow-up at (at most) finitely many points $B=\{a_1,\dots, a_N\}$ and
either (i) $u_k\to u_\infty$ in $W^{1,p}_{loc}(\mathbb{R}\setminus B)$ and
$K_ke^{u_k} \stackrel{*}{\rightharpoondown} K_\infty e^{u_\infty}+ \sum_{j=1}^N
\pi \delta_{a_j}$, or (ii) $u_k\to-\infty$ uniformly locally in
$\mathbb{R}\setminus B$ and $K_k e^{u_k}\stackrel{*}{\rightharpoondown}
\sum_{j=1}^N \alpha_j \delta_{a_j}$ with $\alpha_j\ge \pi$ for every $j$. This
result, resting on the geometric interpretation and analysis provided in a
recent collaboration of the authors with T. Rivi\`ere and on a classical work
of Blank about immersions of the disk into the plane, is a fractional
counterpart of the celebrated works of Br\'ezis-Merle and Li-Shafrir on the
$2$-dimensional Liouville equation, but providing sharp quantization estimates
($\alpha_j=\pi$ and $\alpha_j\ge \pi$) which are not known in dimension $2$
under the weak assumption that $(K_k)$ be bounded in $L^\infty$ and is allowed
to change sign.