The Standard Cosmological Model |

**In General**
> s.a. cosmology [general issues]; cosmological parameters;
general-relativistic cosmology; teaching.

* __Idea__:
It is based on general relativity, homogeneity and isotropy as far as
geometry goes, and on simplified features of the standard model of matter
and interactions, and it includes (0) A quantum gravity Planck era, (i) A
radiation-dominated era (with, or preceded by various possible inflationary
variations), (ii) A matter-dominated era and, based on developments since
1997–1998, (iii) A dark-energy dominated era of late-time acceleration.

* __Status__:
2004–2006, The general consensus favors a ΛCDM model; Together
with a theory of perturbations and baryo- and leptogenesis, it essentially
fits all observations; 2006–2010, There have been claims that there
is evidence for a dynamical dark energy, but the consensus still favors a
minimal six-parameter flat ΛCDM "concordance model", which fits the
WMAP 7-year data and other observations well; 2012, the concordance ΛCDM
model remains the best one to explain the data.

@ __Reviews, status__: Riotto a1010-ln;
Cervantes-Cota & Smoot AIP(11)-a1107;
news Sci(13)mar [confirmation by Planck satellite];
Binétruy yr(14)-a1504-ln [and the theory of fundamental interactions];
Bull et al PDU(16)-a1512 [status and promising directions];
Uzan a1606-ln;
Raveri et al a1606 [knowledge gain];
Lonappan et al a1705 [assessment].

@ __General references__: Zhang et al PRL(07)-a0704 [lensing/matter relationship as test for models];
Szydłowski & Tambor a0805 [effective theory, structural stability];
Bartelmann RMP(10)-a0906;
Gorbunov & Rubakov 10;
Perivolaropoulos JPCS(10)-a1002;
Bean & Tangmatitham PRD(10)-a1002 [constraints on deviations];
Trujillo-Gómez et al ApJ(11)-a1005 [and statistics of galaxies];
de Vega et al a1203 [Chalonge school highlights];
Buchert et al IJMPD(16)-a1512-MG14 [observational challenges of FLRW models].

@ __Tests__: Shafieloo & Clarkson PRD(10)-a0911;
Nesseris & Shafieloo MNRAS(10)-a1004;
Amara & Kitching MNRAS(11)-a1009;
Lombriser PRD(11);
Shi et al MNRAS(12)-a1207 [comparison of models];
Martins AIP(13)-a1212 [rev];
Sapone et al PRD(14)-a1402 [testing the FLRW cosmology].

**Specific Aspects** > see early-universe
cosmology; global geometry and topology;
inflationary cosmology.

**Puzzles and Issues** > s.a. dark energy;
early-universe nucleosynthesis [lithium-7 problem].

* __Issues__:
2004-2006, The universe has a "preposterous content", with direct
observations accounting for only 1% of total density; Plus, the ΛCDM
model has various fudge factors; Could an alternative, "preposterous
theory" like MOND, or some other modification of
Einstein's gravity, be the way to go? Or could the acceleration be the
result of a backreaction to perturbations? How does one carry out the
averaging needed to establish a correspondence between the observed
universe and a homogeneous one (a.k.a. fitting problem).

* __Puzzles and problems__:
2010, There is a mismatch between the amount of lithium-7 predicted from
big-bang nucleosynthesis and the observed amount (2012, Axions might solve
the Li-7 problem); 2013, There are apparent discrepancies with observations
on small galactic scales, which ΛCDM must attribute to complexity in
the baryon physics of galaxy formation; 2014, The "missing satellites" problem
(there are too few satellite galaxies, far fewer than dark matter halos), and
the "planes of satellites" problem (the brightest satellites appear to orbit
their host galaxies on a thin plane); 2017, the Cusp/Core, Missing Satellites,
and Too-Big-to-Fail problems; 2021, The tension between low-redshift (local)
and high-redshift (global) values of the Hubble parameter is not going away.

@ __General references__: Krauss ap/04-ln [dark energy and dark matter];
Scott ap/05-conf;
Primack NPPS(07)ap/06 [ΛCDM, vs MOND and other issues];
Perivolaropoulos a0811-fs [puzzles];
Sami a1401-ln;
McKay & Wiltshire MNRAS(16)-a1503 [the frame of minimum Hubble expansion variance, and the cmb dipole];
Del Popolo & Le Delliou Gal(17)-a1606 [small-scale issues];
Perivolaropoulos & Skara a2105 [challenges].

@ __Low- vs high-redshift measurement tension__:
Wyman et al PRL(14) [neutrinos can help];
Krishnan et al a2105 [does the FLRW model break down?].

@ __Other issues__: Nitti et al PRD(05)ht [initial conditions, naturalness];
Lee a1205
[evidence against ΛCDM from the growth function at different redshifts];
Walker & Loeb CP(14)-a1401 [galaxy scaling relations];
Sawala et al a1412 [simulations resolve the main puzzles];
Bullock & Boylan-Kolchin ARAA(17)-a1707 [small-scale challenges];
> s.a. Flatness Problem; large-scale geometry
and topology; multiverse;
physical constants [cosmology in terms of dimensionless constants];
standard model of particle physics.

@ __Critical views__:
Torretti SHPMP(00);
Lieu a0705;
Sarkar GRG(08)-a0710 [re evidence for dark matter];
Aisenberg 09;
Kundt AIP(09)-a0902;
Narlikar & Burbidge 08 [see also the review];
Kroupa PASA(12)-a1204 [dark matter and the two types of dwarf galaxies];
Janzen a1303-FQXi;
Kodwani a2006-PhD.

**Extensions and Alternatives** > s.a. cosmological
models [pre-Big-Bang, alternatives to inflation]; MOND.

@ __References__:
Khoury a1312-ln [review of extensions];
Wetterich PLB(14)-a1401 [slow freeze];
Joyce et al PRP(15)-a1407 [current state and future developments];
Di Valentino et al PRD(15)-a1507 [12-parameter extension];
Heavens et al PRL(17)-a1704 [no evidence for extensions];
Solà et al a1909 [BD-ΛCDM cosmology].

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