Generalized products and Lorentzian length spaces

Abstract

We construct a Lorentzian length space with an orthogonal splitting on a product $I\times X$ of an interval and a metric space, and use this framework to consider the relationship between metric and causal geometry, as well as synthetic time-like Ricci curvature bounds. The generalized Lorentzian product naturally has a Lorentzian length structure but can fail the push-up condition in general. We recover the push-up property under a log-Lipschitz condition on the time variable and establish sufficient conditions for global hyperbolicity. Moreover we formulate time-like Ricci curvature bounds without push-up and regularity assumptions, and obtain a partial rigidity of the splitting under a strong energy condition.