|  Initial-Value Formulation of General Relativity | 
Based on a Spacelike Hypersurface > s.a. canonical
  formulation and connection variables;
  constraints; Sandwich Conjecture.
  * Idea: We assign the value of
    the 3-metric qab and the
    extrinsic curvature Kab on
    an initial 3D spacelike hypersurface Σ, subject to some constraints, and
    then evolve them and find the full 4-metric in spacetime; If matter is present,
    we assign also the local mass density ρ and current density j,
    assumed to satisfy the energy condition ρ2 ≥
    j aja.
  * Variables: The usual
    dynamical variables are qab and
    Kab, and the choice of gauge is
    represented by the lapse N and shift Na
    (and an initial choice of gauge/coordinates at t = 0);
    > s.a. gauge transformations.
  * Alternatively: One can give,
    on Σ, the distribution and flow of mass-energy, ρ,
    j a and
    Sab, up to a conformal factor,
    and the conformal 3-geometry and its rate of change.
  * Evolution equations:
    For vanishing shift Na = 0,
    the metric and extrinsic curvature (satisfying the constraints) evolve according to
\(\dot q\)ab = 2 N Kab , \(\dot K\)ab = −Da Db N − 2 N Kam Kbm − N KKab − 3Rab N + 8πG N qam qbm(T mn − Tgmn) .
  * Hyperbolic, curvature-based:
    A formulation for arbitrary lapse and shift based on a wave equation for curvature.
   Other approaches: see initial-value
    formalism and approaches [existence and uniqueness, characteristic problem].
 Other approaches: see initial-value
    formalism and approaches [existence and uniqueness, characteristic problem].
References > s.a. constraints for general relativity;
  numerical relativity; Peeling Properties.
  @ General: Stellmacher MA(38)-GRG(10); Bonnor JMM(60) [re uniqueness];
    Choquet-Bruhat & Geroch CMP(69);
    York PRL(71);
    Fischer & Marsden JMP(72);
    York JMP(72),
    PRL(72),
    JMP(73),
    in(79);
    O'Murchadha & York JMP(73),
    PRD(74),
    PRD(74);
    Smarr & York PRD(78);
    Fischer & Marsden in(79);
    Choquet-Bruhat & York in(80);
    York in(82);
    Isenberg FP(86);
    Choquet-Bruhat & York gq/95,
    gq/96;
    York gq/98;
    Friedrich & Rendall LNP(00)gq;
    York proc(06)-gq/04-MGX [qab
      + Kab];
    Chruściel & Friedrich ed-04;
    Brown PRD(05)gq [conformal-traceless].
  @ Intros, reviews: Gourgoulhon gq/07-ln;
    Gourgoulhon 12;
    Isenberg a1304-ch;
    Ringström 13
      [CQG+(15)];
    Minucci a1902-MS.
  @ Hyperbolic: Estabrook et al CQG(97)gq [first-order];
    Yoneda & Shinkai PRL(99)gq/98,
    IJMPD(00)gq/99 [Ashtekar variables];
    Alvi CQG(02)
      [dynamical N and Na];
    Tarfulea PhD(04)gq/05 [constraint-preserving boundary conditions];
    Hilditch & Richter PRD(12) [with Hamiltonian structure];
    Fatibene & Garruto CQG(15)-a1507 [algebraic characterization].
  @ Hyperbolic, curvature-based: Abrahams et al PRL(95)gq,
    CQG(97)gq/96;
    Abrahams & York gq/96;
    Anderson et al gq/97,
    gq/99-proc;
    Choquet-Bruhat et al gq/98-MG8;
    Lau IJMPD(98)gq/96 [based on forms];
    Anderson & York PRL(99)gq.
  @ Other gauges: Andersson & Moncrief AHP(03)gq/01 [elliptic-hyperbolic];
    Paschalidis et al PRD(07)gq/05 [well-posedness].
  @ With matter fields: Husain PRD(99)gq/98;
    Pugliese & Valiente Kroon GRG(13)-a1301 [Einstein-Maxwell-Klein-Gordon system].
  @ Related topics: Durrer & Straumann HPA(88) [applications];
    Frittelli & Reula JMP(99)gq [conformally decoupled];
    Rácz CQG(01)gq [and symmetries];
    Khokhlov & Novikov CQG(02)gq/01 [gauge stability];
    Alcubierre et al PRD(09)-a0907 [with Maxwell fields, and multi-black-holes].
Types of Spacetimes > s.a. minkowski
  spacetime [classical stability]; spherical symmetry;
  types of spacetimes [including stationary].
  @ Black holes: Cole & Valiente Kroon AHP(17)-a1609 [Kerr-Newman  spacetime, geometric invariant];
    > s.a. black holes.
  @ Black-hole binaries: Pfeiffer et al PRD(02)gq [possible initial data];
    Giulini in(03)gq [pedagogical];
    Rácz a1605 [data];
    > s.a. embedding [diagrams].
  @ Asymptotically flat: Penrose PRS(65) [at scri];
    Kánnár CQG(00)gq [with Killing vectors];
    Valiente Kroon CQG(05)gq/04 [near spi and scri],
    PRD(05)gq [Schwarzschildean];
    García-Parrado & Valiente Kroon PRD(07)gq/06 [Schwarzschild spacetime];
    Lopes Costa JPA(10)-a0912 [upper bound for angular-momentum and charge];
    Bäckdahl & Valiente Kroon PRL(10)-a1001,
    AHP(10)-a1005 [deviation from Kerr spacetime].
  @ Conformally flat: Wagh & Saraykar PRD(89);
    Karkowski & Malec gq/04.
  @ Higher-dimensional: Anderson & Tavakol gq/03 [including branes].
  @ Other spacetimes and related topics: Beig LNP(00)gq [Bowen-York initial data];
    Andersson et al AsJM-a1508 [initial data sets with horizons];
    Beig et al a1901 [compact initial data of constant mean curvature];
    > s.a. causality violations; constraints;
gravitating bodies; numerical relativity.
For Other Theories > s.a. higher-order theories;
  scalar-tensor theories; supergravity.
  @ Strong coupling limit: Salopek CQG(98)gq,
    CQG(99)gq/98 [Hamilton-Jacobi].
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