Cosmological Acceleration and Inhomogeneities  

In General > s.a. acceleration [observations, tests]; dark energy; expansion; cosmological models; averaging in cosmology [back-reaction].
* Idea: Attempts to explain the observed acceleration using only general relativity with baryonic and cold dark matter, but by dropping the standard assumption of homogeneity on Hubble scales.
* Timescape cosmology: An approach in which the present age of the universe varies by billions of years according to the position of the observer; A model in which cosmic acceleration is realized as an apparent effect related to the calibration of clocks and rods of observers in bound systems relative to volume-average observers in an inhomogeneous geometry in ordinary general relativity, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the non-linear growth of cosmic structure.
* Void models: The supernova data can be explained if we live near the center of a Hubble-scale void; However, such void models have been shown to be inconsistent with various observations; 2010, They seem to be ruled out by measurements of the kinematic SZ effect; 2012, Loopholes closed; > s.a. cosmological principle.
@ Reviews: Célérier ap/06-proc, ap/07-in; Buchert GRG(08)-a0707; Tomita a0906-conf [assessment]; Tetradis a1002-conf; Räsänen CQG(11)-a1102; Célérier a1203-proc.
@ General references: Dabrowski G&C(02)gq/99; Célérier A&A(00)ap/99; Pascual-Sánchez MPLA(99)gq, gq/99-proc; Bene et al MPLA(06)ap/03; Barausse et al PRD(05)ap; Kolb et al ht/05, Wiltshire gq/05 [primordial inflation]; Moffat ap/05, JCAP(06)ap/05, ap/06; Kolb et al NJP(06)ap/05 [invalidation of no-go results]; Martineau & Brandenberger ap/05; Alnes et al PRD(06)ap/05; Mansouri ap/05; Kai et al PTP(07)gq/06; Leith et al ApJ(08)-a0709; Djorgovskia & Gurzadyan NPPS(07); Paranjape & Singh JCAP(03)-a0801; Larena et al PRD(09)-a0808; Krasiński et al GRG(10)-a0903; Räsänen PRD(10); Kolb CQG(11); Bochner a1109-conf, a1109, IJMPD(13)-a1206 [causal backreaction in a smoothly-inhomogeneous universe]; Romano GRG(13)-a1206; Krasiński PRD(14)-a1309 [ΛCDM model vs Λ = 0 Lemaître-Tolman model]; Skarke PRD(14)-a1310 [acceleration from the distribution of scalar spatial curvature].
@ Timescape: Wiltshire NJP(07)gq, IJMPD(08)-a0712, in(08)-a0712; Wiltshire PRD(09) [test, averages], IJMPD(09)-a0912-FQXi [Cosmological Equivalence Principle]; Smale & Wiltshire MNRAS(11)-a1009 [supernova tests]; Wiltshire a1102-proc; Balasin a1310 [manifest realization]; Wiltshire a1311-proc [rev]; Nazer & Wiltshire PRD(15)-a1410 [cmb anisotropies].
@ Swiss-cheese model: Biswas & Notari JCAP(08)ap/07; Vanderveld et al PRD(08)-a0808; Bene & Csapo a1002.
@ Void models: Caldwell & Stebbins PRL(08)-a0711 [apparent acceleration from local void]; Mattsson GRG(09)-a0711; Quartin & Amendola PRD(10)-a0909 [distinguishing from dark energy]; Kainulainen & Marra AIP(10)-a0911 [small-void + meatball model]; Biswas et al JCAP(10)-a1007 [fitting observations], PRD(10) [as a probe of dark energy]; Moss et al PRD(11)-a1007 [problems with data]; Bolejko & Sussman PLB(11)-a1008 [non-spherical]; Foreman et al PRD(10)-a1009 [spatial and temporal fine-tuning]; Nadathur & Sarkar PRD(11)-a1012 [and the cmb]; Marra & Notari CQG(11)-a1102 [observational constraints]; > s.a. matter; observation [statistics].
@ Dark energy vs underdense void: Moffat a0910.

Arguments Against an Inhomogeneity Effect
* Idea: Some models, notably by Green and Wald, argue that inhomogeneities have a very small backreaction effect on averaged properties of the universe, such as the observed acceleration; Critics claim that those results may be correct under the assumptions used in the arguments, but the assumptions do not capture well the physical situation of interest in cosmology.
@ General references: Geshnizjani et al PRD(05)ap; Flanagan PRD(05)ht; Hirata & Seljak PRD(05)ap; Räsänen CQG(06)ap/05; Siegel & Fry ApJL(05)ap; Ishibashi & Wald CQG(06)gq/05 [general arguments]; Kasai et al PTP(06)ap; Rosenthal & Flanagan a0809; Zibin et al PRL(08)-a0809; Paranjape & Singh PRL(08) [model]; Paranjape PhD(09)-a0906; Ziaeepour a0906 [summary]; Romano JCAP(10)-a0912; Green & Wald PRD(11)-a1011 [framework for effect of perturbations]; Zibin PRD(11) [decaying modes and expected cosmic microwave background spectral distortion].
@ Criticism of arguments: Buchert et al CQG(15)-a1505 & CQG+(16), response Green & Wald a1506, a1601.

Related Topics > s.a. Copernican Principle; inflation; Lemaître-Tolman-Bondi Solutions; Stephani Model.
@ And structure formation: Biswas et al JCAP(07) [non-linear structure formation]; Räsänen IJMPD(08), a0811-proc; Wiegand & Buchert a1103-conf.
@ Effects: Regis & Clarkson GRG(12)-a1003 [and lithium-abundance mismatch]; Buchert a1012-conf [and emerging "morphon" scalar field].
@ From quantum fluctuations: Padmanabhan CQG(05)ht/04; Ringeval et al PRL(10)-a1006 [during inflation]; > s.a. theory of cosmological acceleration.
@ Other models: Hossain a0709 [FLRW islands surrounded by vacuum]; Ishak et al PRD(08)-a0708 [Szekeres model]; Mattsson GRG(10); Collins a1011 [with periodic variation in one direction]; Célérier A&A(12)-a1108 [clarification]; Bueno & Perivolaropoulos PRD(11)-a1110 ["topological quintessence", topological defect formed during a recent phase transition].

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