The spacelike-characteristic Cauchy problem of general relativity in low regularity

Abstract: In this paper we study the spacelike-characteristic Cauchy problem for the Einstein vacuum equations. We prove that given initial data on a maximal compact spacelike hypersurface $\Sigma \simeq \overline{B(0,1)} \subset \mathbb{R}^3$ and the outgoing null hypersurface $\mathcal{H}$ emanating from $\partial \Sigma$, the time of existence of a solution to the Einstein vacuum equations is controlled by low regularity bounds on the initial data at the level of curvature in $L^2$. The proof uses the bounded $L^2$ curvature theorem by Klainerman, Szeftel and Rodnianski, the extension procedure for the constraint equations by Czimek, Cheeger-Gromov theory in low regularity developed by Czimek, the canonical foliation on null hypersurfaces in low regularity by Czimek and Graf, and global elliptic estimates for spacelike maximal hypersurfaces.