Inverse problem for connections in semi-linear wave equations on Lorentzian manifolds

This paper recovers Hermitian connections of semi-linear wave equations with cubic nonlinearity. The main novelty is in the geometric generality: we treat the case of an arbitrary globally hyperbolic Lorentzian manifold. Our approach is based on microlocal analysis of nonlinear wave interactions, which recovers a non-abelian broken light-ray transform, and the inversion of broken light-ray transforms on globally hyperbolic Lorentzian manifolds.