Next Contents Previous

4.2. CDM models for structure formation

The elements discussed so far assemble into the LambdaCDM cosmological model, which is the simplest possibility that is consistent with current evidence. The overall matter power spectrum is written dimensionlessly as the logarithmic contribution to the fractional density variance, sigma2:

Equation 91 (91)

which undergoes linear growth

Equation 92 (92)

where the linear growth law is D(a) = a g[Omega(a)] in the matter era, and the growth suppression factor for a density parameter Omegam neq 1 is

Equation 93 (93)

The transfer function Tk depends on the dark-matter content as discussed earlier, in particular displaying a horizon-scale break at k appeq 0.06(Omegam h)-1 h Mpc-1. Weak oscillatory features are also expected if the universe has a significant baryon content. Eisenstein & Hu (1998) give an accurate fitting formula that describes these wiggles. This detailed fit of the CDM spectrum is to be preferred to the older notation in which the spectrum was described by the zero-baryon form, but with an effective value of Omegam h that allowed for the main effects of the baryon content:

Equation 94 (94)

(Sugiyama 1995).

Next Contents Previous