Parameter Control of Binary Black Hole Initial Data

When solving Einstein’s equations for Binary Black Holes (BBH) numerically, we must first find initial data on a three-dimensional spatial slice. In the extended conformal thin-sandwich (XCTS) decomposition, this initial data problem is cast as five elliptic partial differential equations. Prior to solving the XCTS equations, we have to choose “free data” that impose boundary conditions and specify background quantities. After solving the XCTS system, we can measure the black hole masses and spins, as well as asymptotic quantities like total linear momentum. Typically, we want to choose these physical quantities before running a BBH simulation, but they can only be measured after numerically solving the XCTS equations. In this talk, we will explain how we address this using an iterative scheme in SpECTRE, a task-based parallel code that aims to simulate BBH for the new generations of gravitational wave detectors. We will also compare this approach with the one taken in the predecessor code, SpEC.