|  Cosmological Constant | 
In General > s.a. cosmological-constant phenomenology;
  cosmological-constant problem; dark-energy models;
  mach's principle; vacuum.
  * History: Introduced by
    Einstein in 1917 to obtain static universes.
  $ Def: A constant Λ
    representing a vacuum energy density, introduced in the action of general
    relativity or the Einstein equation, respectively,
∫M (R − 2Λ) dv, Rab − \(1\over2\)R gab + Λ gab = 8πG Tab .
  * In quantum field theory:
    Usually considered to be due to zero-point energy (as pointed out by Zel'dovich
    in 1968), but in some proposals arises from its fluctuations; Required by symmetry
    breaking in the early universe, Hawking's picture of spacetime foam, or the gauged
    SO(n) of extended supergravity.
  * In quantum gravity:
    The ground state for a spacetime with non-zero Λ, to the extent that it is
    understood, is (Anti-)de Sitter spacetime; A common handwaving argument for the
    natural value of Λ in quantum gravity is that dimensional considerations lead to
    lP−2, but
    arguments of the fluctuation type can also be made assuming that each spacetime element contributes
    an amount lP−2
    to the Lagrangian density but with a fluctuating sign.
Variable Cosmological Constant, Λ as a Field
  > s.a. non-commutative gravity; unimodular
  gravity; newton's gravitational constant.
  @ General references:
    Gasperini PLB(87),
    CQG(88) [thermal approach];
    McGuigan PRD(90)
      [quantum, from t = (det q)1/2];
    van Putten gq/98 [consequences];
    Burdyuzha et al ap/99;
    Novello et al CQG(01)ht/00;
    Elizalde PLB(01),
    Caldwell ap/02 [from Casimir effect];
    Donoghue JHEP(03) [gradients];
    Shapiro et al PLB(03);
    Ahmed et al PRD(04)ap/02,
    Ahmed IJMPA(05)-proc [causal sets and statistical fluctuations],
    comment Volovik JETPL(04)gq and
    Barrow PRD(07)gq/06;
    Hsu & Zee MPLA(05) [Planck mass and size of universe];
    Barceló JETPL(07)gq/06;
    Antoniadis et al NJP(07)gq/06 [dynamical screening by quantum field theory effects];
    Xu et al a0905,
    PLB(10)-a0905;
    Yoon a0906;
    Ahmed & Sorkin PRD(13)-a1201;
    Mäkelä PRD(13);
    Solà IJMPD(15)-a1505-GRF [and cosmological entropy];
    Smolin CQG(16)-a1507 [as conjugate variable to Newton's constant];
    Chernyavsky & Hajian CQG(18)-a1710 [as a conserved charge, thermodynamic approach];
    Cree et al PRD(18)-a1805;
    Alexander et al a1807 [conjugate to Chern-Simons invariant];
    > s.a. special relativity [de Sitter version].
  @ Self-tuning: Kim & Lee PLB(04)ht/03;
    Kim JPCS(10)-a1009;
    Sobral-Blanco & Lombriser PRD(20)-a2003 [local mechanism].
  @ Relaxation: Brown & Teitelboim PLB(87) [dynamical neutralization];
    Štefančić PLB(09)-a0807 [from inhomogeneous equation of state];
    Porto & Zee CQG(10)-a0910,
    MPLA(10)-a1007-proc [extreme ultra-IR];
    Bauer et al PLB(09)-a0902,
    PLB(10)-a0912,
    Bauer et al CQG(10) [perturbations],
    JCAP(10)-a1006,
    Alberte et al JHEP(16)-a1608 [dynamical relaxation].
  @ And cosmology: Novello et al CQG(02) [from chiral anomaly];
    Aldrovandi et al G&C(05)gq/03;
    Shapiro & Solà ap/04-talk;
    Borges & Carneiro GRG(05)gq [decaying vacuum density];
    Ma NPB(08)-a0708 [and constraints];
    Basilakos et al PRD(09)-a0907 [expansion and structure formation];
    Xu MPLA(10) [varying in time, from renormalization group];
    Barrow & Shaw PRL(11)-a1007,
    GRG(11)-a1105-GRF,
    Solà JPCS(11)-a1102 [and the cosmological-constant problem];
    Romano & Chen JCAP(11)-a1104-GRF [corrections from local inhomogeneities];
    Biswas et al a1105-conf [beginning with Λ < 0];
    Bisabr IJMPD(18)-a1803 [decay from gravitational coupling and expansion of the universe].
  @ Running, scale dependence: Kosower MPLA(89);
    Bhattacharya et al PLB(00);
    Bonanno & Reuter JCAP(07) [from renormalization group, and cosmology];
    Foot et al PLB(08)-a0712 [does not run with renormalization scale];
    Shapiro & Solà a0808,
    PLB(09)-a0910 [it may run];
    Capozziello & Funkhouser MPLA(09)-a0812 [scaling law];
    Velasquez-Toribio IJMPD(12)-a0907 [and perturbations];
    Ward MPLA(10) [in quantum gravity];
    Hamber & Toriumi IJMPD(13)-a1301 [running would be inconsistent with general covariance];
    Markkanen PRD-a1412 [curvature-induced];
    Solodukhin PLB(16)-a1509 [and UV divergences in quantum gravity];
    Viaggiu a2102 [quantum fluctuations and renormalization].
  @ From fluctuations: Sorkin IJTP(97)gq;
    Gurzadyan & Xue MPLA(03)ap/01;
    Padmanabhan CQG(02)gq,
    CQG(05)ht/04 [and quantum gravity];
    Volovik JLTP(01)gq,
    in(03)gq;
    in Dreyer ht/04;
    Jejjala & Minic IJMPA(07)ht/06;
    Elizalde JPA(07) [non-trivial topology and braneworld boundary conditions];
    Sorkin AIP(07)-a0710 [causal set discreteness];
    Wang et al a0806 [quantum fluctuations of spacetime];
    Santos a0902,
    PLA(09)-a0912;
    Katti et al CQG(09)-a0904
      [analogy with surface tension of a fluid membrane];
    Broda & Szanecki AdP(10)-a0910-proc;
    Maggiore PRD(11)-a1004;
    Santos ASS(11)-a1006;
    de Cesare et al PLB(16)-a1603 [stochastic fluctuations of Newton's constant];
    Hoga a1804-GRF [from first principles];
    Viaggiu CQG(18)-a1810,
    PS(19)-a1908;
    > s.a. cosmic acceleration.
  @ From condensate: Dymnikova & Khlopov MPLA(00) [evaporating Bose condensate];
    Alexander & Vaid ht/06,
    ht/07 [chiral fermions in FLRW spacetime];
    Finazzi et al a1204-proc [analog-gravity point of view];
    Das & Bhaduri a1812 [ultralight bosons].
References > s.a. general-relativity
  solutions; higher-order gravity.
  @ General: Einstein SPAW(17);
    Hawking in(82),
    PTRS(83);
    Banks NPB(85);
    Coughlan et al NPB(89) [and dilatations];
    Strominger NPB(89) [Lorentzian quantum cosmology];
    Fiziev gq/00-talk [and dilatonic gravity];
    Earman SHPMP(03) [conceptual];
    Aldrovandi et al IJMPD(04)gq [and fundamental physics];
    Beck PhyA(09) [axiomatic approach];
    Dadhich Pra(11)-a1006;
    Solà IJMPA(16)-a1612 [and dynamical vacuum energy].
  @ History: Harvey PT(07)apr [Schrödinger and Einstein];
    Calder & Lahav A&G(08)-a0712 [early precursors, Newton];
    Kragh a1111/AHES [precursors];
    Harvey a1211;
    Kragh & Overduin 14;
    Lahav fs(17)-a1704;
    O'Raifeartaigh et al EPJH(18)-a1711 [rev];
    Novosyadlyj EPJH(18)-a1712;
    Cohen-Tannoudji Metr(18)-a1802-conf;
    O'Raifeartaigh & Mitton PiP(18)-a1804;
    O'Raifeartaigh PT(18)oct.
  @ Reviews: Bernstein & Feinberg ed-89;
    Weinberg RMP(89),
    ap/96;
    Sahni & Starobinsky IJMPD(00)ap/99;
    Harvey & Schücking AJP(00)aug [Einstein];
    Carroll LRR(01)ap/00;
    Peebles & Ratra RMP(03)ap/02;
    Padmanabhan PRP(03)ht/02;
    Bousso GRG(08)-a0708-ln;
    Martin CRAS(12)-a1205.
  @ I: Maddox Nat(89)feb;
    Mellor SP(89); Goldsmith 95;
    Krauss & Turner SA(04)sep.
  @ And field theory: Schützhold PRL(02) [QCD trace anomaly];
    Sundrum PRD(04)ht/03 ["fat" gravity and cosmological-constant suppression];
    Moffat gq/03 [graviton as bound state],
    gq/03-proc;
    Mashhoon & Wesson CQG(04)gq [5D];
    Mukohyama  PRD(04) [radiative corrections and stability];
    Blasone et al BJP(05)ht/04 [neutrino mixing];
    Volovik JETPL(05)gq-in [from macroscopic parameters];
    Mahajan et al PLB(06)ap [Casimir effect: not from zero-point energy];
    Ram a0705,
    Demir FP(09)-a0910 [as zero-point energy];
    Álvarez & Vidal a1007-wd [imaginary part];
    Ziaeepour MPLA(12)-a1205;
    Garattini a1212-proc
      [effects of modified dispersion relations and non-commutative geometry];
    > s.a. brans-dicke theory;
      de sitter space [stability]; standard model.
  @ As integration constant: Padmanabhan IJMPD(06)gq;
    Cook a0810;
    Banks & Fischler a1811 [as an infrared boundary condition];
    Manfredi GRG(21)-a2102 [as an eigenvalue];
    > s.a. modified general relativity; unimodular gravity.
  @ Other origin: Lee et al JCAP(07)ht [entanglement energy];
    Jackson & Hogan IJMPD(08)ht/07 [unconventional quantum spin-statistics];
    Panković et al a0712 [holography, surface energy density];
    Dale et al a0906 [vector-tensor gravity, vector-field energy density];
    Azri & Bounames GRG(12)-a1007 [from 8D hypercomplex manifold];
    Capozziello & Luongo Entr(11)-a1010 [from entangled states];
    Kiefer et al CQG(11)-a1010 [from scalar field decoherence];
    Charmousis et al JHEP(17)-a1704 [holographic self-tuning];
    Asselmeyer-Maluga & Król PDU(18)-a1709 [from small exotic \({\mathbb R}^4\)s];
    Le Delliou & Lorca PDU(20)-a1906 [topological];
    Gaztañaga MNRAS(21)-a2101 [boundary term in the action];
    Perez & Sudarsky GRG(21)-a1911 [energy momentum diffusion in discrete spacetime];
    > s.a. cosmic acceleration; topology change.
  @ And higher dimensions: Wesson FPL(06)gq/04 [vacuum instability];
    Bauer PhD(06)ht [discrete extra dimensions];
    Soni et al a1509 [compact  dimensions].
  @ And quantum gravity: Garattini gq/04,
    a0910-proc [as Sturm-Liouville eigenvalue];
    Capozziello & Garattini CQG(07)gq
      [as eigenvalue of Wheeler-DeWitt equation for f(R) theory];
    Garattini JPA(08)-a0712-conf;
    Garattini PRD(09)-a0912 [in Hořava gravity];
    Yurov et al a1212 [as Sturm-Liouville eigenvalue];
    Govaerts & Zonetti PRD(13)-a1212 [lessons from 2D dilaton gravity];
    Miković & Vojinović a1407 [in a Regge state-sum model];
    Majid & Tao a1412 [non-commutative geometry];
    Dvali & Gómez a1412 [quantum exclusion of a positive cosmological constant];
    Hamada & Matsuda PRD(16)-a1511 [two-loop corrections];
    Padmanabhan IJMPD(16)-a1603,
    a1702-conf [microstructure of spacetime];
    Ng a1706-proc [different methods];
    Gryb & Thébault PLB(18)-a1801 [superpositions];
    Perez et al IJMPD(18)-a1804 [in terms of noisy diffusion of energy to Planck scale];
    Cremaschini & Tessarotto Symm(18)-a1807;
    Zhang et al a2101 [lqg, regularization];
    Koberinski FP(21)-a2101 [regularization];
    > s.a. instantons; quantum gravity
      and cosmology [wormholes]; spacetime geometry in quantum gravity
      and spin-foam models.
  @ Related topics: Zel'dovich JETPL(67) [and elementary particles];
    Gasperini PLB(89) [and spacetime dimension];
    Henneaux & Teitelboim PLB(89) [and time];
    Louko CQG(91) [discontinuity at Λ = 0?];
    Datta IJMPD(96) [non-gravitating];
    Aldrovandi & Barbosa gq/02 [and Lorentz group Casimir];
    Aldrovandi et al FP(03) [Λ → ∞];
    Mersini-Houghton gq/06 [arrow of time forbids Λ > 0];
    Mazur ap/07 [from "gravitational atoms"];
    Romano et al EPL(14)-a1311 [effect of primordial curvature perturbations];
    Davidson & Rubin PRD(14)-a1401 [Λ = 0 in normalized general relativity];
    > s.a. category theory; emergent gravity.
  > Online resources:
    see Wikipedia page. 
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