|  Bianchi Spacetime Models of Type IX | 
In General
  > s.a. chaos in bianchi models; gravitational
  instanton; minisuperspace quantum cosmology.
  $ Def: In the Lie-algebra
    classification, nij
    = (+1, +1, +1), vi =
    0; The group G is (the simply connected covering group of) SO(3).
  * History: The
    Russian school (BKL) started studying Bianchi IX in 1962, hoping to
    understand the behavior of the metric near a generic singularity
    (introduced map for u); Misner started in 1966, but using
    earlier work on Taub-NUT, hoping to understand anisotropy dissipation
    (introduced Hamiltonian and potential).
  * Special cases: \(l_1 = l_2 = l_3
    = {1\over2}\,R\), FLRW models; Kasner solution; Taub-NUT solution; Diagonal models,
    the metric has gab
    = diag(l1, l2,
    l3), with li
    functions of time; The diagonal vacuum model is also called Mixmaster universe.
  * Geometry: 3V
    = 16π2 l1
    l2 l3,
ω1 = cosψ dθ + sinψ sinθ dφ , ω2 = sinψ dθ − cosψ sinθ dφ , ω3 = dψ + cosθ dφ .
* Evolution: Well approximated by a sequence of Bianchi I (Kasner) epochs; Each one is characterized by the value of a parameter u, which gives rise to an approximate discrete dynamics, the Gauss map
un+1 = (un − [un])−1 ;
    In the Hamiltonian approach, each epoch is the time between two bounces
    off the potential; At each bounce, two scale factors switch between
    expansion and contraction, while the third one keeps contracting; An
    era is a set of epochs with the same two factors switching
    behavior, i.e., bouncing off the same pair of walls.
  * Better approximation: & Garfinkle.
References
  > s.a. gravitational energy-momentum; types
  of spacetime singularities; Taub-NUT Solution [early work].
  @ General: Harvey PRD(83) [new solutions];
    Montani et al IJMPA(08)-a0712 [classical and quantum, review].
  @ ADM approach: Misner ApJ(68),
    PR(69),
    PRL(69);
    in Misner et al 73;
    in Ryan & Shepley 75;
    Imponente & Montani gq/02-in,
    IJMPD(02).
  @ BKL approach:
    Belinskii et al AiP(70),
    JETP(71),
    AiP(82);
    Manojlović & Miković JMP(00)mp [Painlevé III];
    Imponente & Montani JKPS(03)gq/02.
  @ Other approach:
    Creighton & Hobill in(94) [Ellis-MacCallum-Wainwright];
    Gogilidze et al G&C(97) [Hamiltonian, non-diagonal].
  @ Dynamics near the singularity:
    Czuchry & Piechocki PRD(13)-a1202 [non-diagonal models];
    Czuchry et al a1409 [comparing diagonal and non-diagonal cases];
    Parnovsky & Piechocki a1605;
    Kiefer et al EPJC(18)-a1807 [simplified dynamics, numerical simulations].
  @ Other dynamics:
    Llibre & Valls JMP(05),
    JMP(06) [Darboux first integrals];
    Buzzi et al JPA(07);
    Starkov PLA(11) [compact
      invariant sets; no periodic, homoclinic, or heteroclinic orbits in the zero-level set of the Hamiltonian];
    Dimakis et al PRD(19)-a1809 [Liouville integrability];
    Barrow a2006 [synchronisation of oscillations];
    > s.a. chaos in bianchi models;
      early-universe models.
  @ Self-dual:
    Tod PLA(94);
    Chakravarty & Ablowitz PRL(96);
    Maszczyk CQG(96).
  @ Self-similar: Apostolopoulos & Tsamparlis GRG(03)gq.
  @ Isotropization: Guzman IJTP(96);
    Bergamini et al PRD(97)gq/96 [inflation];
    Cervantes-Cota & Chauvet PRD(99)gq/98 [induced gravity];
    Kirillov & Montani PRD(02)gq [and inflation];
    Battisti et al a0903-proc [semiclassical mechanism].
  @ With matter: Waller PRD(84) [electromagnetism];
    Banerjee et al ASS(90) [viscous fluid];
    Toporensky & Ustiansky gq/99,
    Fay & Lehner GRG(05)gq [massive scalar];
    Farajollahi & Ravanpak IJTP(09)-a1001 [massless scalar];
    Saha G&C(13)-a1107 [restrictions on the components of the energy-momentum tensor];
    Pavluchenko PRD(16)-a1607 [Einstein-Skyrme];
    Saha CJP(18)-a1705 [spinor field];
    > s.a. types of spacetimes [instability].
  @ Collapse:
    Lin & Wald PRD(90) [recollapse];
    Charters a1106
      [vacuum, proof of collapse conjecture].
  @ In Hořava-Lifshitz gravity:
    Myung et al PRD(10)-a0911 [chaotic and non-chaotic solutions],
    JHEP(10)-a1001;
    Bakas et al CQG(10)-a0911 [and chaos];
    Misonoh et al PRD(11)-a1104.
  @ Other theories:
    Belinskii et al PLB(78),
    in Cotsakis 90 [Euclidean];
    Barrow & Dąbrowski PRD(98)ht/97 [low-energy string theory];
    Garcia de Andrade & Monerat ap/01/C&G [with torsion];
    Halpern GRG(03)gq/02 [5D];
    van den Hoogen et al PRD(03)gq/02 [brane];
    Bergshoeff et al CQG(03)ht [supergravity];
    Maceda et al PRD(08) [non-commutative];
    > s.a. modified uncertainty relations;
      non-commutative gravity.
  @ Related topics: Chitre PRD(72) [wave equation];
    Hu PRD(73) [Klein-Gordon fields];
    King PRD(91);
    in Misner in(94) [as geodesic motion];
    Berger et al CQG(97)gq/96,
    gq/97-conf [other algorithms];
    Cotsakis et al PRD(98)gq/97 [adiabatic invariants and catastrophes];
    Barguine et al PRD(01)
      [with cosmological constant, homoclinic structure];
    Battisti & Montani a0903-proc [gup approach];
    Shabbir et al G&C(10) [proper curvature collineations].
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