For the Warm Dark Matter ( WDM ) cosmological model the implications of strongly inhomogenous , primordial baryon distribution on sub-galactic scales for Big Bang Nucleosynthesis , Cosmic Microwave Background anisotropies and Galaxy Formation ( including fully non-linear evolution to z =0 ) are discussed , and the inflationary theory leading to such distributions is briefly reviewed .
It is found that Big Bang Nucleosynthesis is essentially unaffected relative to SBBN and that the change in recombination history at z~ { } \sim~ { } 1500 - 700 relative to “ standard ” theory leads to differences in the anisotropy and polarization power spectra , which should be detectable by the Planck satellite provided systematic effects can be accounted for .
Moreover , it is shown by fully cosmological , hydro/gravity simulations that the formation of galactic discs is only weakly affected by going from smooth to highly non-homogenous , initial baryon distributions .
In particular , the final disc angular momenta at z =0 are as large as for the standard case and the “ disc angular momentum problem ” is solved to within a factor of two or better without invoking ( hypothetical ) energetic feedback events .
A very desirable difference relative to the the standard WDM model , however , is that the on-set of star ( and AGN ) formation happens earlier .
For the “ optimal ” free-streaming mass scale of M _ { f } ~ { } \sim~ { } 1.5 ~ { } \cdot~ { } 10 ^ { 11 } ~ { } h ^ { -1 } ~ { } M _ { \odot } the redshift of formation of the first stars increases from z _ { \mathrm { *,i } } =4-5 to \ga 6.5 , in much better agreement with observational data on high-redshift galaxies and QSOs .
It will , however , not be possible to push z _ { \mathrm { *,i } } 
above \approx 10 , because at higher redshifts the gas velocity field is nowhere compressive .
Probing the “ dark ages ” will hence enable a direct test of this theory .