An inverse scattering problem for the Klein-Gordon equation with a classical source in quantum field theory

Abstract

An inverse scattering problem for a quantized scalar field $\mathbf{\varphi }$ obeying a linear Klein-Gordon equation $(\square + m^2 + V) {\bm ϕ} = J \mbox{in $\mathbb{R} \times \mathbb{R}^3$}$ is considered, where $V$ is a repulsive external potential and $J$ an external source $J$. We prove that the scattering operator $\mathcal{S}=\mathcal{S}(V,J)$ associated with $\mathbf{\varphi }$ uniquely determines $V$. Assuming that $J$ is of the form $J(t,x)=j(t)\rho (x)$, $(t,x)\in \mathbb{R}\times {\mathbb{R}}^3$, we represent $\rho$ (resp. $j$) in terms of $j$ (resp. $\rho$) and $\mathcal{S}$.