Well-posed constraint-preserving boundary conditions for the AA formulation of Einsteinʹs equations

In this paper, we address the problem of artificial boundary conditions for the symmetric linearized hyperbolic formulation of Einsteinʹs equations introduced in [A.M. Alekseenko, D.N. Arnold, New first-order formulation for the Einstein equations, Phys. Rev. D (3) 68 (6) (2003) 064013, 6 pp.]. We prescribe simple boundary conditions that make the problem well-posed and preserve the constraints.