The point-like limit for a NLS equation with concentrated nonlinearity in dimension three

TL;DR

This paper rigorously justifies the point-like limit of a 3D nonlinear Schrödinger equation with concentrated nonlinearity by analyzing a regularized nonlocal model and showing its convergence to a point interaction model.

Contribution

It provides the first rigorous derivation of a nonlinear point interaction limit from a regularized nonlocal NLS in three dimensions.

Findings

The regularized dynamics converges to a point interaction model as the cutoff vanishes.

The model captures the nonlinear effects at a point in three dimensions.

The approach confirms the well-posedness and properties of the limiting dynamics.

Abstract

We consider a scaling limit of a nonlinear Schr\"odinger equation (NLS) with a nonlocal nonlinearity showing that it reproduces in the limit of cutoff removal a NLS equation with nonlinearity concentrated at a point. The regularized dynamics is described by the equation \begin{equation*} i\frac{\partial }{\partial t} \psi^\varepsilon(t)= -\Delta \psi^\varepsilon(t) + g(\varepsilon,\mu,|(\rho^\varepsilon,\psi^\varepsilon(t))|^{2\mu}) (\rho^\varepsilon,\psi^\varepsilon(t)) \rho^\varepsilon \end{equation*} where $\rho^{\varepsilon} \to \delta_0$ weakly and the function $g$ embodies the nonlinearity and the scaling and has to be fine tuned in order to have a nontrivial limit dynamics. The limit dynamics is a nonlinear version of point interaction in dimension three and it has been previously studied in several papers as regards the well-posedness, blow-up and asymptotic properties of solutions. Our result is the first justification of the model as the point limit of a regularized dynamics.