Symmetry-breaking mechanism for the Z4 general-covariant evolution system -: art. no. 064036

The general-covariant Z4 formalism is further analyzed. The gauge conditions are generalized with a view to numerical relativity applications and the conditions for obtaining strongly hyperbolic evolution systems are Given both at the first and the second order levels. A symmetry-breaking mechanism is proposed that allows one, when applied in a partial way, to recover previously proposed strongly hyperbolic formalisms, like the BSSN and the Bona-Masso formulas. When applied in its full form, the symmetry-breaking mechanism allows one to recover the full five-parameter family of first order KST systems. Numerical codes based in the proposed formalisms are tested. A robust stability test is provided by evolving random noise data around Minkowski space-time. A strong field test is provided by the collapse of a periodic background of plane Gravitational waves, as described by the Gowdy metric.