CAUCHY-CHARACTERISTIC EVOLUTION OF EINSTEIN-KLEIN-GORDON SYSTEMS

A Cauchy-characteristic initial value problem for the Einstein-Klein-G ordon system with spherical symmetry is presented. Initial data are sp ecified on the union of a spacelike and null hypersurface. The develop ment of the data is obtained with the combination of a constrained Cau chy evolution in the interior domain and a characteristic evolution in the exterior, asymptotically flat region. The matching interface betw een the spacelike and characteristic foliations is constructed by impo sing continuity conditions on metric, extrinsic curvature, and scalar field variables, ensuring smoothness across the matching surface. The accuracy of the method is established for all ranges of M/R, most nota bly, with a detailed comparison of invariant observables against refer ence solutions obtained with a calibrated, global, null algorithm.