Uniqueness of excited states to $-\Delta u+u-u^3=0$ in three dimensions

TL;DR

This paper proves the uniqueness of excited states for a nonlinear PDE in three dimensions by analyzing the corresponding ODE with rigorous numerical methods, revealing all smooth radial solutions with specific zero counts.

Contribution

It establishes the uniqueness of excited states in a nonlinear PDE using a novel combination of analytical inequalities and rigorous numerical verification.

Findings

All excited states with specific zero counts are unique.

The solutions tend to zero at infinity.

The method combines analytical inequalities with numerical verification.

Abstract

We prove the uniqueness of several excited states to the ODE $\ddot y(t) + \frac{2}{t} \dot y(t) + f(y(t)) = 0$, $y(0) = b$, and $\dot y(0) = 0$ for the model nonlinearity $f(y) = y^3 - y$. The $n$-th excited state is a solution with exactly $n$ zeros and which tends to $0$ as $t \to \infty$. These represent all smooth radial nonzero solutions to the PDE $\Delta u + f(u)= 0$ in $H^1$. We interpret the ODE as a damped oscillator governed by a double-well potential, and the result is proved via rigorous numerical analysis of the energy and variation of the solutions. More specifically, the problem of uniqueness can be formulated entirely in terms of inequalities on the solutions and their variation, and these inequalities can be verified numerically.