Constraint propagation of c²-Adjusted equations - Another recipe for robust evolution systems

We focus the formulation problem in numerical relativity, propose new sets of evolution equations, and demonstrate some numerical tests. The goal is to construct a robust evolution system against numerical instability during long-term numerical integration in strong gravitational field. One key idea is to adjust the evolution equations with constraint terms, as was systematically formulated by Yoneda and Shinkai. We here apply an adjusting method proposed by Fiske (2004) which uses the norm of constraints, C², and does not require the background metric for specifying effective Lagrange multipliers. We present sets of evolution equations both in ADM and BSSN formulations and show numerical tests using Gowdy wave propagation. Detail analyses are in progress, but we observe constraint damping effect as expected.