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3+1 formalism and bases of numerical relativity - LUTh ...

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6 CONTENTS<br />

8 The initial data problem 125<br />

8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125<br />

8.1.1 The initial data problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125<br />

8.1.2 Conformal decomposition <strong>of</strong> the constraints . . . . . . . . . . . . . . . . . 126<br />

8.2 Conformal transverse-traceless method . . . . . . . . . . . . . . . . . . . . . . . . 127<br />

8.2.1 Longitudinal/transverse decomposition <strong>of</strong> Âij . . . . . . . . . . . . . . . . 127<br />

8.2.2 Conformal transverse-traceless form <strong>of</strong> the constraints . . . . . . . . . . . 129<br />

8.2.3 Decoupling on hypersurfaces <strong>of</strong> constant mean curvature . . . . . . . . . . 130<br />

8.2.4 Lichnerowicz equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130<br />

8.2.5 Conformally flat <strong>and</strong> momentarily static initial data . . . . . . . . . . . . 131<br />

8.2.6 Bowen-York initial data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136<br />

8.3 Conformal thin s<strong>and</strong>wich method . . . . . . . . . . . . . . . . . . . . . . . . . . . 139<br />

8.3.1 The original conformal thin s<strong>and</strong>wich method . . . . . . . . . . . . . . . . 139<br />

8.3.2 Extended conformal thin s<strong>and</strong>wich method . . . . . . . . . . . . . . . . . 141<br />

8.3.3 XCTS at work: static black hole example . . . . . . . . . . . . . . . . . . 142<br />

8.3.4 Uniqueness <strong>of</strong> solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144<br />

8.3.5 Comparing CTT, CTS <strong>and</strong> XCTS . . . . . . . . . . . . . . . . . . . . . . 144<br />

8.4 Initial data for binary systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145<br />

8.4.1 Helical symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146<br />

8.4.2 Helical symmetry <strong>and</strong> IWM approximation . . . . . . . . . . . . . . . . . 147<br />

8.4.3 Initial data for orbiting binary black holes . . . . . . . . . . . . . . . . . . 147<br />

8.4.4 Initial data for orbiting binary neutron stars . . . . . . . . . . . . . . . . 149<br />

8.4.5 Initial data for black hole - neutron star binaries . . . . . . . . . . . . . . 150<br />

9 Choice <strong>of</strong> foliation <strong>and</strong> spatial coordinates 151<br />

9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151<br />

9.2 Choice <strong>of</strong> foliation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152<br />

9.2.1 Geodesic slicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152<br />

9.2.2 Maximal slicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153<br />

9.2.3 Harmonic slicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159<br />

9.2.4 1+log slicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161<br />

9.3 Evolution <strong>of</strong> spatial coordinates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162<br />

9.3.1 Normal coordinates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162<br />

9.3.2 Minimal distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163<br />

9.3.3 Approximate minimal distortion . . . . . . . . . . . . . . . . . . . . . . . 167<br />

9.3.4 Gamma freezing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168<br />

9.3.5 Gamma drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170<br />

9.3.6 Other dynamical shift gauges . . . . . . . . . . . . . . . . . . . . . . . . . 172<br />

9.4 Full spatial coordinate-fixing choices . . . . . . . . . . . . . . . . . . . . . . . . . 173<br />

9.4.1 Spatial harmonic coordinates . . . . . . . . . . . . . . . . . . . . . . . . . 173<br />

9.4.2 Dirac gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

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