Acceleration of the Cosmological Expansion Rate  

In General blue bullet s.a. inhomogeneities and other proposed explanations.
* 1998: Two teams (High-z Supernova Search Team and Supernova Cosmology Project) published results showing that, contrary to standard wisdom, the universal expansion is accelerating, from observation of the redshift-luminosity distance relationship for 80 supernovae out to z = 0.8.
* 2002: Acceleration parameter q0 = –0.56 ± 0.04; Many models proposed, most assuming that the current acceleration began at z ≤ 1.
* 2004: Chandra observations confirm that the acceleration began about 6 Gyr ago.
* 2007: SNLS 3rd year data to be released with 250 new supernovae, SNAP mission will yield about 2000 supernovae per year and will be able to exclude many proposed explanations.
* 2008: ESSENCE results for over 200 type Ia SNe in the range 0.2 < z < 0.8 are consistent with a cosmological constant.
* 2009: Data seem to favor a scenario in which expansion is slowing down again, but are consistent with a cosmological constant.
* 2011: Nobel Prize in physics awarded to Saul Perlmutter, Adam Riess, and Brian Schmidt [@ news PT(11)dec, comment PT(12)feb].
* 2013: Discrepancy between global (cmb) and local measurements of the Hubble constant, and more evidence for q < –1.
@ Non-technical: Ostriker & Steinhardt SA(01)jan; Riess & Turner SA(04)feb [onset]; news pw(07)dec, Krauss pw(07)dec, Crease pw(07)dec [X anniversary]; Krauss & Scherrer SA(08)mar; news msnbc(11)sep [acceleration could be an illusion]; news sa(16)apr [faster acceleration?].
@ Reviews: Filippenko PASP(01)ap; Schmidt CQG(02); Leibundgut & Sollerman EPN(02)ap/02; Perlmutter PT(03)apr; Shapiro & Turner ApJ(06)ap/05 [without general relativity]; Perivolaropoulos ap/06-conf; Durrer & Maartens GRG(08)-a0711; Frieman AIP(08)-a0904; Goldhaber a0907-proc [history]; Brax a0912-ln; Bean a1003-ln; Blanchard A&A(10)-a1005 [evidence and status]; Huterer a1010-ch; Sapone IJMPA(10); Schwarz et al PPNP(11)-a1012-conf; Clocchiatti a1112-proc; Weinberg et al PRP(13)-a1201; Astier & Pain CRAS(12)-a1204 [evidence]; Astier RPP(12)-a1201 [and supernovae]; Sami & Myrzakulov CS-a1309-talk; Baltay IJMPD(14).
@ General references: Mannheim PRD(98)ap [theoretical implications], ap/98-proc; Sidharth in(00)hp/98; Starkman et al PRL(99)ap; Straumann EJP(99)ap; Turner ap/99-proc; Liddle NAR(01)ap/00; Updike PT(05)apr; Rapetti et al MNRAS(07)ap/06 [kinematical study]; Cattoën & Visser gq/07 [the case is less watertight than usually assumed]; Daly & Djorgovski AIP(07)-a0710; Bolejko & Andersson JCAP(08)-a0807 [apparent and average acceleration]; Lima et al a0905 [independent method]; Bull & Clifton PRD(12)-a1203 [local and non-local measures of acceleration in inhomogeneous models]; Pavón IJGMP(14) [and entropy increase]; Tutusaus et al A&A(17)-a1706 [low-redshift probes are consistent with a non-accelerated universe].

@ General references: Riess et al AJ(98)ap; Perlmutter et al ApJ(99)ap/98, ap/98-conf, PRL(99)ap [the original results]; Gong & Wang PRD(06) [constraints]; Albrecht AIP(07)-a0710 [the case for an aggressive observational program]; Sherwin et al PRL(11) [from cmb alone]; Sutherland MNRAS(12)-a1105 [test using baryon acoustic oscillations]; Tsagas PRD(11)-a1107 [peculiar motions, apparent acceleration and dipole anisotropy]; Darling ApJL(12)-a1211, Yu et al PRL(14) [towards a direct measurement using 21-cm line redshifts]; Amendola & Euclid Theory Working Group LRR(13) [upcoming Euclid mission]; Frieman PT(14)apr [upcoming Dark Energy Survey of 200 million galaxies].
@ Supernovae: Drell et al ApJ(00)ap/99; Gott et al ApJ(01)ap/00; Riess PASP(00)ap; et al ApJ(01)ap; Filippenko LNP(04)ap/03; Jain & Ralston ApJ(06)ap/05; SNAP ap/05-rp [goals]; Gong et al JCAP(07), Seikel & Schwarz JCAP(08)-a0711, JCAP(09) [model-independent evidence]; Leibundgut GRG(08)-a0802; Cattoen & Visser PRD(08)-a0809, a0906-proc [treat data with some caution]; Krisciunas a0809 [results of ESSENCE survey]; Perlmutter RMP(12) [Nobel lecture]; Howell AS(13); Haridasu et al a1702 [strong evidence].
@ 2016 controversy: Nielsen et al SRep(16)-a1506, Nielsen a1508-MS [marginal evidence for acceleration]; Rubin & Hayden ApJL(16)-a1610, Ringermacher & Mead a1611 [the evidence for acceleration is strong].
@ Galaxies: Guzzo et al Nat(08)-a0803 [redshift surveys]; Marinoni & Buzzi Nat(10)nov [Alcock–Paczyński Nat(79)oct geometric test applied to pairs of galaxies].
@ Gravitational waves: Seto et al PRL(01)ap [0.1 Hz, proposal]; Yagi et al JCAP(12)-a1112 [and inhomogeneous models vs ΛCDM].
@ Anisotropy search: Cooke & Lynden-Bell MNRAS(10)-a0909 [inconclusive]; Antoniou & Perivolaropoulos JCAP(10)-a1007, Cai & Tuo JCAP(12)-a1109 + news PhysOrg(11)sep [evidence for preferred axis]; Zhao et al IJMPD(13)-a1305; Javanmardi et al ApJ(15)-a1507 [some evidence]; Bernal et al PLB(17)-a1606 [evidence]; > s.a. dark energy.
@ Related topics: Faraoni PDU-a1508 [turnaround radius].

Change in Acceleration > s.a. cosmological expansion [expansion history].
* 2005: There is some evidence for oscillations in the Hubble expansion history.
* 2006, 2009: There is clear statistical evidence for a late time transition from a decelerating to an accelerating phase.
* 2010: Articles reporting evidence of a present slowing down of the cosmic acceleration, and possible current deceleration.
* Theory: LambdaCDM with the currently preferred cosmological density Ω0 and cosmological constant ΩΛ, predicts that the Universe expansion decelerates down to redshift z ~ 0.9 and accelerates at later times; Conformal gravity predicts that the cosmic expansion has always been accelerating.
@ Theory: Blandford ap/04-proc [jerk and equation of state]; Ponce de León IJMPD(06)gq/05 [model]; Popławski PLB(06)gq [in f(R) gravity]; Kim & Yoon PLB(06)gq [2D non-commutative dilaton model]; Melchiorri et al PRD(07)-a0706 [beginning of acceleration]; Linder PRD(10)-a1006 [acceleration as an occasional phenomenon]; Hu et al ApJ-a1509 [slowing down of cosmic acceleration].
@ Data: Lazkoz et al JCAP(05)ap [snIa Gold data set fit]; John ApJ(05)ap, Elgarøy & Multamäki JCAP(06)ap [past deceleration, Bayesian analysis]; Ishida et al APP(08)-a0706 [beginning of acceleration]; Daly et al ApJ(08)-a0710; Shafieloo et al PRD(09)-a0903 [slowdown? data and interpretation]; Blomqvist et al JCAP(10)-a1006 [data consistent with no fluctuations]; Li et al JCAP(10)-a1011 [combination of data]; Wu & Yu a1012 [evidence for present deceleration]; Carvalho & Alcaniz MNRAS(11)-a1102 [from the expansion rate H(z)]; Diaferio et al JCAP(11)-a1103 [using GRBs as probes]; news lbl(12)mar [BOSS measurement of the era when acceleration set in]; Rest et al ApJ(14)-a1310 [PanSTARRS1 data indicate that q < –1]; Odderskov et al JCAP(14)-a1407 [discrepancy in values of H0 exceeds expected variance].

Differing Points of View
* Suggestions: 2002, Supernovae may look dimmer because photons turn into axions along the way.
@ References: Loeb ApJL(98)ap [deceleration!]; Csáki et al PRL(02) [axions]; Narlikar et al PASP(02)ap [alternative]; Mészáros ApJ(02)ap [statistical, premature]; Sawicki ap/02 [R < 0]; Vishwakarma MNRAS(03)ap; Choudhuri ap/06 [Thomson scattering]; Middleditch ap/06 [supernovae, no acceleration]; Arp a0712 [deceleration and variable particle masses]; Vishwakarma & Narlikar RAA(10)-a1010; Skarke a1508 [as an optical illusion].

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