Thomas-Fermi Limit for the Cubic-quintic Schrödinger Energy with Radial Potential (2410.14300v1)

Abstract: In this paper, we consider the cubic-quintic Schr\"{o}dinger energy function with radial trapping potential \begin{gather*} \begin{aligned} {E}(\varPhi)=\frac{1}{2}\int_{\mathbb{R}^d}\left(|\nabla \varPhi|^2+V(x)|\varPhi|^2\right)\,dx +\frac{\kappa}{4}\int_{\mathbb{R}^d}|\varPhi|^4\,dx +\frac{1}{6}\int_{\mathbb{R}^d}|\varPhi|^6\,dx, \end{aligned} \end{gather*} where $d=1,2,3$ and the parameter $\kappa=\pm1$. We mainly focus on the ground state under the mass constraint $\int_{\mathbb{R}^d}|\varPhi|^2\,dx=N$, in the Thomas-Fermi limit where the particle number $N$ tends to $\infty$. In contrast to previous approaches, we utilize an \emph{energy method} to go beyond the classical Thomas-Fermi approximation used in the Gross-Pitaevskii energy functional or Ginzburg-Landau functional. Firstly, we show that the ground state has the limit behaviors as $N\to+\infty$, which corresponds to a Thomas-Fermi limit. The limit profile is given by the Thomas-Fermi minimizer $u^{TF}(x)=\left[\mu^{TF}-C_0|x|^p\right]^{\frac{1}{4}}_{+}$, where $\mu^{TF}$ is a suitable Lagrange multiplier with exact value. Moreover, we obtain a sharp vanishing rate for ground states $\varphi_N$ that $|\varphi_{N}|{L^{\infty}(\mathbb{R}^d)}\sim N^{-\frac{d}{2d+p}}$ as $N\to+\infty$. The gradient squared non-integrable property of the Thomas-Fermi minimizer at the boundary $\partial B(\sqrt[p]{\mu^{TF}/C_0})$, in the vicinity of which the ground state has irregular behavior in the form of a steep \emph{corner layer}. Finally, let $\tau=N^{-\frac{2}{2d+p}}$ ($\to0^+$ as $N\to+\infty$), we prove that $\left|\tau^{-d/2}\varphi{N}(\cdot/{\tau})-u^{TF}\right|_{L^\infty}\leq O\left( \tau^{\sigma-\epsilon}|\ln \tau|^{-\epsilon}\right)$ in $B\left( \sqrt[p]{\mu^{TF}/C_0}-\left( \tau|\ln \tau|\right)^\epsilon\right)$ as $\tau\to0^+$, where $\sigma=\min{p-\alpha,1}$ and $0<\epsilon\leq\sigma/2$.