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The **Lambda-CDM model** (**ΛCDM** or **LCDM**)
is a current, widely-used "working model" (**standard model**)
of Big Bang/dark matter/dark energy cosmology.
It includes cold dark matter and a
cosmological constant (Lambda or Λ).
The cosmological constant provides an explanation
for the universe's observed accelerating expansion.
Dark matter provides an explanation for
the dynamics of galaxies and galaxy clusters
that appear to have more gravitational attraction
than their EMR can explain.
(Other explanations for these phenomena include deviations
in the behavior of gravity and/or dynamics from accepted models.)
Lambda-CDM relates many observed phenomena to six apparently arbitrary
parameters determinable from observation.
Some values determined in 2015 using Planck data:

parameter | symbol | determined value |

physical baryon density | Ω_{b}h² | 0.02230 |

physical dark matter density | Ω_{d}h² | 0.1188 |

age of the universe | t_{0} | 13.799 × 10^{9} years |

scalar spectral index | n_{s} | 0.9667 |

curvature fluctuation amplitude | Δ²_{R} | 2.441 × 10^{-9} |

optical depth to the epoch of reionization (EOR) | τ | 0.066 |

(Values from other determinations do not match these exactly, but
the differences are small.)
The six parameters cited may not be those listed above, but in
combination, they would be equivalent to the above through relations
assumed by the model.
For example, the *optical depth to reionization* represents
a measure of how long ago the EOR took place,
which is also sometimes cited as a redshift (z ~ 11).
**h** (in *h²* above) indicates the (dimensionless) **Hubble parameter**,
which is the universe's expansion expressed as a fraction of
100 km s^{-1}Mpc^{-1}, which varies with time.
Some additional values calculable from the six:

item | symbol | calculated value |

Hubble constant | H_{0} | 67.74 km s^{-1} Mpc^{-1} |

baryon density parameter | Ω_{b} | 0.0486 |

dark matter density parameter | Ω_{d} | 0.2589 |

matter density parameter | Ω_{m} | 0.3089 |

dark energy density parameter | Ω_{Λ} | 0.6911 |

The density parameters are expressed as fractions of the critical density.
The dark matter density parameter is sometimes cited
as Ω_{c}, presumably for *cold* dark matter,
but that symbol is also sometimes used to refer to the
critical density parameter.

http://en.wikipedia.org/wiki/Lambda-CDM_model

https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.cfm

https://ui.adsabs.harvard.edu/abs/2016A%26A...594A..13P/abstract

https://ui.adsabs.harvard.edu/abs/2020A%26A...641A...6P/abstract

alternative cosmologies

angular power spectrum

astronomical quantities

Bolshoi simulation

cold dark matter (CDM)

core-cusp problem

cosmological simulation

D56

dark matter

dark matter halo

dwarf galaxy problem

Einstein-de Sitter model

epoch of galaxy formation

galaxy formation

initial fluctuations

redshift-angular size relation

standard model