On the Geometry of Null Cones to Infinity Under Curvature Flux Bounds

The main objective of this paper is to control the geometry of a future outgoing truncated null cone extending smoothly toward infinity in an Einstein-vacuum spacetime. In particular, we wish to do this under minimal regularity assumptions, namely, at the (weighted) L^2-curvature level. We show that if the curvature flux and the data on an initial sphere of the cone are sufficiently close to the corresponding values in a standard Minkowski or Schwarzschild null cone, then we can obtain quantitative bounds on the geometry of the entire infinite cone. The same bounds also imply the existence of limits at infinity of the natural geometric quantities. Furthermore, we make no global assumptions on the spacetime, as all assumptions are applied only to this single truncated cone. In our sequel paper, we will apply these results in order to control the Bondi energy and the angular momentum associated with this cone.