Proposed Explanations of the Cosmological Acceleration  

In General > s.a. acceleration [observations]; dark energy; expansion; cosmological models; inflation; relativistic cosmological models.
* Explanations: They include a cosmological constant, quintessence or other fields (e.g., k-essence), modified gravity (such as f(R) theories), inhomogeneities (not ruled out yet despite many arguments against it) and the giant void hypothesis (violation of the Copernican Principle), semiclassical effects, trans-Planckian fluctuations, or anti-friction in CDM, and some form of antigravity; Observations can discriminate between them (for example, a cosmological constant implies dw/dz = 0, quintessence dw/dz > 0 and k-essence dw/dz < 0); Another class of explanations is that some physics (e.g., non-linear electromagnetism) affects the observed redshift-luminosity relationship we see for a given expansion history.
* Status: 2005, Kolb et al suggested that the acceleration is due to super-horizon inhomogeneities from primordial fluctuations; 2006, The consensus seems to be that inhomogeneity effects may be present, but they are too small; 2007, Model suggests that inhomogeneities can also partly mimic an acceleration by affecting light propagation; 2009, Observations are still consistent with a cosmological constant; 2016, Comparison after Planck 2015, in order of decreasing ability to explain the observations (Bayesian criteria based on the JLA sample of type-Ia supernova observations, the Planck 2015 distance priors of cosmic microwave background, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant):
(1) Cosmological constant model.
(2) Generalized Chaplygin gas model, constant w model, α dark-energy model.
(3) Holographic dark energy model, new generalized Chaplygin gas model, Chevalliear-Polarski-Linder model.
(4) New agegraphic dark energy model, Dvali-Gabadadze-Porrati model, Ricci dark energy model.
@ Reviews and general: Carroll AIP(04)ap/03; Szydłowski et al PLB(06)ap [top 10 models]; Bludman IJMPD(08); Uzan GRG(07)ap/06; Silva e Costa & Makler ap/07 [relationships]; Ruíz-Lapuente CQG(07)-a0704; Frieman et al ARAA(08)-a0803; Durrer & Maartens in(10)-a0811; Sami a0901-in; Caldwell & Kamionkowski ARNPS(09)-a0903; Silvestri & Trodden RPP(09)-a0904; Clifton & Ferreira SA(09)apr [giant void]; Brax a0912-ln; Basilakos PASP-a1001 [constraints]; Induráin PhD(09)-a1002 [as window to new physics]; Park et al PRD(10)-a1003 [unified framework]; Tsujikawa MPLA(10); Sapone IJMPA(10)-a1006; Jiménez et al IJMPA(12)-a1107 [effective theory]; Bolotin et al PU(12)-a1108; Trodden a1212-conf; Bloomfield et al JCAP(13)-a1211 [effective field theory]; Trodden a1604-proc; Xu & Zhang EPJC(16)-a1607 [comparison of 10 models after Planck 2015]; Ryan a2104-PhD.
@ And thermodynamics: Radicella & Pavón GRG(12)-a1012; Easson et al PLB(11) [entropic proposal].

blue bullet  Main proposals: see cosmological constant; modified gravity [and quantum effects].

Other Proposals > s.a. inhomogeneities [including timescape]; large-scale topology; quintessence; topological defects; variation of constants.
@ General references: Trentham MNRAS(01)ap [assumptions]; Amendola MNRAS(03)ap/02 [at z > 1]; Rendall LNP(06)gq/04 [accelerating solutions]; Notari MPLA(06)ap/05 [unjustified formulation]; Avelino et al PRD(06)ap [not cosmic domain wall network]; Ortiz IJMPD-a2011.
@ Scalar fields: Rodgers & Yasuda IJMPA(07)ht/06 ["diffeomorphism scalar field"]; Kehagias JPCS(07)ht/06 [non-conventional scalar]; Bieli in(08)ap/06 [non-minimal]; Castro FP(07) [scalar for Weyl invariance]; Bhattacharya et al PRD(10)-a0911 [massless, inhomogeneous].
@ Vector fields, electromagnetism: Novello et al PRD(04)ap/03 [non-linear electromagnetism]; González-Díaz in(06)ht [subquantum cmb photon potential]; Jiménez & Maroto a0807-proc [vector field], AIP(10)-a0911 [electromagnetic extra mode]; Kruglov PRD(15)-a1601, IJMPD(16)-a1603, IJMPA(16)-a1607 [non-linear electromagnetism]; Novello & Hartmann IJMPA(19)-a1903 [non-minimally coupled]; Kruglov IJMPA(20)-a2009 [non-linear electrodynamics].
@ Fluids: Pinto & Fraga GRG(08) [ordinary fluids]; Gagnon & Lesgourgues JCAP(11)-a1107 [bulk viscosity]; Balthazar & Ferreira PRD(15)-a1407 [from the effective field theory of a perfect fluid].
@ Other fields: Wigmans ap/02-wd [neutrinos], ap/04/PRL [neutrino degeneracy pressure]; Schwarz ap/02-conf [imperfect CDM]; Holdom JHEP(04)ht [Goldstone ghost]; Beck ap/05-proc [modified standard model, chaos]; Ribas et al PRD(05) [fermions]; Balakin & Dehnen PLB(09)-a0910 [self-interacton]; Grams et al CQG(14)-a1407 [fermions]; Smoller et al a1412 [standard-model instability].
@ Particle interactions: Aldrovandi et al gq/05; Díez-Tejedor & Feinstein PLA(06); Steigman et al JCAP(09)-a0812, Lima et al PRD(12)-a1205 [gravitationally-induced particle creation]; Berezhiani et al PRD(17)-a1612 [coupling between dark and ordinary matter].
@ Other proposals: Goldberg PLB(00) [chiral phase transition]; Zimdahl et al PRD(01)ap/00 [anti-friction]; Beck PRD(04)ap/03 [chaotic quantum field theory]; Oliveira & Hartnett FPL(06)ap [Carmeli's cosmology]; Bonanno et al CQG(06) [crossover phenomenon]; Ne'eman IJMPA(06) ["recoil of the mass-making"]; Hammond & Pilling a0806 [gravitating entropy]; Gough a0906 [star formation]; Temple & Smoller PNAS(09) + news seed(09)sep [wave of expansion]; Brown et al JCAP(10)-a0909 [gravitational waves]; Koivisto et al PRD(11)-a1006 [anisotropic curvature]; Obregón & Quirós PRD(11)-a1108 [non-commutative effects]; Ernest a1202-conf ["quantum expansion parameter"]; Shen & Xue a1802 [large-scale Lorentz violation]; > s.a. exotic differentiable structures; fractals in physics; fractional calculus; holography; K-Essence; tachyons; topological acceleration.

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