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## Main Question or Discussion Point

Short intro.: I'm a M.Sc. student finishing up a thesis on DM from a HEP aspect. My background in particle physics is ok, but I have had a lot of trouble with the cosmology aspects. Any help would be appreciated since I can't seem to find clear, concise answers for them with references (maybe the answers are necessarily long).

1) Why do people tend to use little h in place of H for Hubble's constant. And what's with the units? To make it of order unity? To embed error? (read that somewhere)

2) Why is the relic density expressed as omega h^2 instead of simply omega? And why as a fraction of the critical density as opposed to the actual total density? That last question is probably a result of a very weak knowledge of FLRW but I feel I should ask.

3) I've heard several times about the analysis of the CMB to obtain the matter-energy content of the universe using a multipole expansion on the power spectrum. The units seem quite confusing and perhaps I should review basic multipole expansion, but I can't seem to see a simple way to understand the basic analysis. If this necessitates a good reference, please recommend me one.

Thanks!

Shiro

1) Why do people tend to use little h in place of H for Hubble's constant. And what's with the units? To make it of order unity? To embed error? (read that somewhere)

2) Why is the relic density expressed as omega h^2 instead of simply omega? And why as a fraction of the critical density as opposed to the actual total density? That last question is probably a result of a very weak knowledge of FLRW but I feel I should ask.

3) I've heard several times about the analysis of the CMB to obtain the matter-energy content of the universe using a multipole expansion on the power spectrum. The units seem quite confusing and perhaps I should review basic multipole expansion, but I can't seem to see a simple way to understand the basic analysis. If this necessitates a good reference, please recommend me one.

Thanks!

Shiro