Inverse scattering problems for non-linear wave equations on Lorentzian manifolds

Spyros Alexakis, Hiroshi Isozaki, Matti Lassas, Teemu Tyni

Published 2024-11-14Version 1

We show that an inverse scattering problem for a semilinear wave equation can be solved on a manifold having an asymptotically Minkowskian infinity, that is, scattering functionals determine the topology, differentiable structure and the conformal type of the manifold. Moreover, the metric and the coefficient of the non-linearity are determined up to a multiplicative transformation. The manifold on which the inverse problem is considered is allowed to be an open, globally hyperbolic manifold which may have bifurcate event horizons or several infinities (i.e., ends) of which at least one has to be of the asymptotically Minkowskian type. The results are applied also for FLRW space-times that have no particle horizons. To formulate the inverse problems we define a new type of data, non-linear scattering functionals, which are defined also in the cases when the classically defined scattering operator is not well defined. This makes it possible to solve the inverse problems also in the case when some of the incoming waves lead to a blow-up of the scattered solution.