Wave equation with concentrated nonlinearities

TL;DR

This paper introduces a nonlinear wave operator with concentrated nonlinearities, analyzes the associated wave equation, and provides explicit solutions and blow-up behavior for specific cases, advancing understanding of nonlinear wave dynamics with point interactions.

Contribution

It defines a new nonlinear operator for wave equations with point interactions and analyzes existence, uniqueness, and blow-up phenomena in this context.

Findings

Explicit solution formulas for the nonlinear wave equation.

Existence and uniqueness results for Lipschitz nonlinearities.

Analysis of blow-up mechanisms when the interaction set is a singleton.

Abstract

In this paper we address the problem of wave dynamics in presence of concentrated nonlinearities. Given a vector field $V$ on an open subset of $\CO^n$ and a discrete set $Y\subset\RE^3$ with $n$ elements, we define a nonlinear operator $\Delta_{V,Y}$ on $L^2(\RE^3)$ which coincides with the free Laplacian when restricted to regular functions vanishing at $Y$, and which reduces to the usual Laplacian with point interactions placed at $Y$ when $V$ is linear and is represented by an Hermitean matrix. We then consider the nonlinear wave equation $\ddot \phi=\Delta_{V,Y}\phi$ and study the corresponding Cauchy problem, giving an existence and uniqueness result in the case $V$ is Lipschitz. The solution of such a problem is explicitly expressed in terms of the solutions of two Cauchy problem: one relative to a free wave equation and the other relative to an inhomogeneous ordinary differential equation with delay and principal part $\dot\zeta+V(\zeta)$. Main properties of the solution are given and, when $Y$ is a singleton, the mechanism and details of blow-up are studied.