|  Kaluza-Klein Theories | 
In General > s.a. higher-dimensional gravity.
  * Idea: A (4+k)-dimensional
    general relativity (with matter in extended versions), and the usual Einstein-Hilbert
    action; The extra dimensions have to be all spacelike, otherwise one gets arbitrarily
    large causality violations and negative 4D energy density; The non-abelian theories
    often have torsion, if they include fermions.
  * Dimensional reduction:
    An effective 4D theory can be obtained in a natural way if there are Killing
    vector fields along the extra dimensions; One gets gravity coupled to fields
    coming from the extra metric components (or, if there were already matter fields,
    they end up coupled to gauge fields); If there are no Killing vector fields, one
    does a harmonic mode expansion – this of course is coordinate-dependent;
    There are ambiguities in the choice of fields in 4D; Jordan proposed to solve them
    by experiment; usually it is done getting some desired form for the action;
    > s.a. spacetime models.
  * Motivation: (1) One gets from
    a purely metric theory all the known interactions in 4D; The field strengths
    are components of the higher-dimensional Christoffel symbols; To get strong
    and electroweak interactions, one needs at least 11D; (2) Internal charges
    coupled to gauge fields are treated on the same footing as energy-momentum;
    (3) It arises naturally in supergravity theories; (4) Possible spacetime
    dependence of the gravitational and fine-structure constants (this really
    depends on the 4D interpretation adopted); (5) Lowering of GUT scale from
    1016 to 103 GeV,
    if the internal dimension is large enough (> see branes).
  * Problems: Chiral fermions (ok if
    there are matter fields); Renormalizability (as usual for gravity); Failure to
    reproduce quantum numbers of particles; Appearance of huge mass terms.
Early Work
  * History: Kaluza suggested
    the use of an extra dimension; Klein that it be compactified.
  @ "Constant internal radius": Nordström
    PZ(14)phy/07,
    OFVSF(14)phy/07,
    OFVSF(15)phy/07;
    Kaluza SPAW(21)-a1803;
    Einstein & Grommer SUBH(23);
    Klein ZP(26);
    Einstein SPAW(27), SPAW(27);
    Klein ZP(28);
    Einstein & Rosen PR(35);
    Einstein & Bergmann AM(38);
    Einstein, Bargmann & Bergmann in(41);
    Einstein & Pauli AM(43).
  @ Variable radius: Jordan AN(48);
    Thiry CR(48), JMPA(51);
    in Lichnerowicz 55;
    Klein HPAS(56);
    Jordan ZP(59);
    in Wheeler 62;
    in DeWitt 65;
    Rayski APP(65);
    Kerner AIHP(68).
  @ Non-Abelian: in DeWitt 65;
    Kerner AIHP(68);
    Trautman RPMP(70).
  @ History: in Pais 82;
    Krym TMP(99)gq/98;
    O'Raifeartaigh & Straumann RMP(00)hp/98;
    Straumann gq/00-MG9 [Pauli and non-abelian Kaluza-Klein];
    van Dongen SHPMP(02)gq/00 [Einstein 1938–1943];
    Ravndal a1309 [Oskar Klein's contributions];
    Peruzzi & Rocci a1811 [Einstein's 1927 papers];
    > s.a. higher-dimensional gravity.
And Other Higher-Dimensional Theories
  > s.a. branes; higher-dimensional gravity;
  teleparallel theories.
  @ Kaluza-Klein modes in brane world: Gu ap/03 [Kaluza-Klein bursts and cosmic rays].
  @ With extra timelike dimensions: Yndurain PLB(91);
    Iglesias & Kakushadze PLB(01)ht/00;
    Ellis gq/01 [5D Kaluza-Weyl space].
  @ With no extra dimensions: Pavšič PLB(05)ht/04,
    IJMPA(06)gq/05 [Clifford space].
  @ Non-commutative: Madore in(89)-a1510 [supplementary factor in the algebra],
    PRD(90);
    Madore & Mourad ht/96;
    Besnard a1902;
    > s.a. non-commutative geometry.
  @ Higher-order gravity theories: Maeda & Dadhich PRD(07)ht/06,
    Molina & Dadhich IJMPD(09)-a0804 [Einstein-Gauss-Bonnet gravity];
    Dehghani & Assyyaee PLB(09)-a0811 [third-order Lovelock gravity, and dark energy];
    Başkal & Kuyrukcu GRG(13)-a1004 [dimensional reduction].
  @ Other variations: Cianfrani & Montani a0904-proc [based on an averaging procedure];
    Kalinowski EPJC(14)-a1401,
    FdP(16)-a1410 [non-symmetric gravity];
    Stoica IJMPD(16)-a1601 [degenerate metric, zero-length extra dimensions];
    Collion & Vaugon a1709 [non-Ricci-flat geometries, including matter].
Special Aspects
  > see ADM formulation; black
  holes; CPT; energy
  positivity; models and phenomenology;
  spacetime topology and topology change.
  @ Reduction: Grumiller & Jackiw IJMPD(06)mp [conformally flat spaces];
    Lacquaniti & Montani MPLA(09)-a0906 [5D];
    Gauntlett et al JHEP(09) [D = 11 supergravity];
    Chopovsky et al AHEP(13)-a1311 [Ricci-flat internal spaces and absence of KK particles].
General References
  > s.a. particle physics; spacetime.
  @ I: Kaku 94.
  @ Textbooks and reviews: Hermann 78;
    Ferrara & Ellis 82;
    de Sabbata  & Schmutzer 83;
    Chodos CNPP(84);
    Mecklenburg FdP(84);
    Lee 84;
    Freund PhyD(85);
    Piran & Weinberg ed-86;
    Appelquist et al ed-87;
    Bailin & Love RPP(87);
    Blau et al in(87);
    Coquereaux & Jadczyk 88;
    Duff ht/94;
    Overduin & Wesson PRP(97)gq/98;
    Wesson 99 [5D];
    Cianfrani & Montani a0904-proc.
  @ Mathematical aspects: Wesson MPLA(95) [Killing vector fields and covariance];
    Betounes JGP(04) [Rab].
  @ Related topics: Keyl CQG(97) [quantum field theory on Kaluza-Klein background];
    Kane PT(98)may [fiction];
    de Assis et al G&C(00) [loop variables];
    Ponce de León G&C(02) [equation of motion];
    Starks et al IJTP(06) [5D, geometric formulation];
    Reifler & Morris a0707 [equivalence with Yang-Mills theory];
    Lukman et al NJP(11)-a1001 [effective two-dimensionality].
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