|  Spin-Coefficient Formalism | 
NP Formalism (Newman-Penrose)
  > s.a. Edth Operator; gravitational
  instanton; tetrads.
  * Idea: A formalism
    that recasts the non-linear, second-order Einstein equation as a set
    of first-order, mostly linear equations for a set of spin connection
    coefficients, by a systematic use of null tetrads.
  * Advantages: It makes
    transparent the Petrov type of the space, and the Bianchi identities
    become particularly simple and tractable.
  * Applications: It has become
    a standard tool for finding exact solutions, solving wave equations in
    curved backgrounds, studying black-hole perturbations (see Chandrasekhar's
    book), and analyzing the asymptotic structure of gravitational fields at
    null infinity.
  @ General references:
    Newman & Penrose JMP(62),
    PRL(65);
    Pirani in(65);
    in Misner et al 73, 870–871;
    Penrose & Rindler 84,
    86;
    in Wald 84, §13.2;
    Law JGP(09)-a0802 [4D neutral metrics];
    Bäckdahl CQG(09)-a0905 [constants in terms of Geroch-Hansen multipole moments];
    Nerozzi a1109 [new approach, in transverse tetrads];
    Papadopoulos a1707 [finding integrals and identities];
    Gómez & Quiroga a1711 [rev];
    Barnich et al a1910 [and the BMS current algebra].
  @ For Riemannian metrics: Goldblatt GRG(94).
  @ And Lanczos potential: Andersson & Edgar JMP(00)gq/98.
  @ And Sparling forms: Frauendiener GRG(90).
  @ Invariants of Riemann spinor: Haddow GRG(96)gq/95.
  @ For 3D Riemannian  manifolds: Aazami JGP-a1410 [and results on hypersurface-orthogonal vector fields and curvature].
Individual Coefficients > s.a. weyl tensor.
  * Idea: 12 complex quantities
    that replace the 24 real Ricci rotation coefficients of an orthonormal tetrad
    when one uses a null one; In an asymptotically flat space time, there is a
    natural choice of tetrad in the asympototic region for which the Weyl scalars
    fall off at different powers of r.
  – Ψ0:=
    Cabcd la
    mb lc
    md,
    Transverse radiation propagating along
    la.
  – Ψ1:=
    Cabcd
    la
    mb
    lc
    nd, Longitudinal radiation
    propagating along la;
    Pure gauge.
  – Ψ2:=
    Cabcd
    la
    mb
    m*c
    nd,
    "Mass aspect", the Coulomb part of the field.
  – Ψ3:=
    Cabcd
    la
    nb
    m*c
    nd,
    Longitudinal radiation propagating along
    na; Pure gauge.
  – Ψ4:=
    Cabcd m*a
    nb m*c
    nd, Transverse radiation
    propagating along na;
    Falls off most slowly.
GHP Formalism (Geroch, Held & Penrose)
  * Idea: A variation
    of the Newman-Penrose spin-coefficient formalism.
  @ General references:
    Geroch, Held & Penrose JMP(73);
    Edgar & Ludwig GRG(96), GRG(97),
    GRG(97)gq [integration],
    GRG(00);
    Held GRG(99).
  @ Related topics: Ludwig & Edgar CQG(00) [generalized Lie derivative];
    Carminati  & Vu GRG(01),
    GRG(03) [Maple package].
Applications and Variations
  > s.a. horizons; perturbations of FLRW models.
  @ Special spacetimes: Bruni et al AIP(05)gq/04 [in astrophysical relativity];
    Wu & Shang CQG(07) [stationary];
    Zhang et al PRD(09) [stationary electrovacuum];
    > s.a. kerr-newman solutions.
  @ Higher dimensions: Ortaggio et al CQG(07)gq [Ricci identities];
    Durkee et al CQG(10)-a1002 [GHP formalism];
    García-Parrado Gómez-Lobo & Martín-García
      JMP(09),
    JPCS(11)-a1102 [5D];
    Ortaggio et al CQG(13)-a1211 [rev].
  @ Variations: Law JGP(09) [four-dimensional neutral metrics].
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  send feedback and suggestions to bombelli at olemiss.edu – modified 31 oct 2019