Dimensionless power spectrum and density contrast

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Maximilian Jokel
Posts: 1
Joined: July 25 2014
Affiliation: Technische Universität München

Dimensionless power spectrum and density contrast

Post by Maximilian Jokel » July 29 2014

Hello,

I have started working with CAMB only recently and consequently have some questions.

1.) I have already managed to get the matter power spectrum for different values of the density parameters [tex]\Omega_\text{c}[/tex] and [tex]\Omega_\text{m}[/tex], but there is one problem: Setting the density parameter [tex]\Omega_\text{c}=0[/tex] the programm compains about crazy values. Of course, this value isn't realistic at all but I need the power spectrum for a universe containing only baryons and no cold dark matter. Is there any possibility how to avoid this error message?


2.) Besides this I also need the dimensionless power spectrum [tex]k^3P_\delta(k)[/tex] where [tex]P_\delta(k)[/tex] is the matter power spectrum. What do I have to do to get it?


3.) Furthermore I need the gravitational potential [tex]\Phi(a)[/tex] as well as the density contrast [tex]\delta(a)[/tex]. Where do I get them from?


Since I am still very little versed I ask you to respond as fully and understandable as possible for me as a beginner. Of course I have read the CAMB notes but they are not very enlightening from my questions.


Thanks,
Maximilian

Jim Zibin
Posts: 4
Joined: July 26 2010
Affiliation: University of British Columbia

Dimensionless power spectrum and density contrast

Post by Jim Zibin » August 04 2014

For 2.), CAMB should give you a file called something like ...matterpower.dat. The first column is [tex]k/h[/tex] in units of [tex]\rm{Mpc}^{-1}[/tex]. The second column is [tex]h^3P_\delta(k)[/tex] in units of [tex]\rm{Mpc}^3[/tex], where [tex]P_\delta[/tex] is the dimensionful power spectrum.

For 3.), if you want the power spectrum of the potential, presumably you just need to use the Poisson equation to translate.

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