CAMB: Matter power spectrum output

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Aaron Fenyes
Posts: 4
Joined: August 09 2006
Affiliation: University of Michigan

CAMB: Matter power spectrum output

Post by Aaron Fenyes » October 21 2006

Does anyone know whether the wavenumbers in CAMB matter power spectra are 2pi / (comoving distance) or 2pi / (some other distance)?

Antony Lewis
Posts: 1941
Joined: September 23 2004
Affiliation: University of Sussex
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Re: CAMB: Matter power spectrum output

Post by Antony Lewis » November 05 2006

Pretty much everything in CAMB is comoving. Note output matter power spectra are in h Mpc^{-1} units.

Aaron Fenyes
Posts: 4
Joined: August 09 2006
Affiliation: University of Michigan

CAMB: Matter power spectrum output

Post by Aaron Fenyes » November 17 2006

Weird... it says in Peacock's Cosmological Physics that
Regarding [tex]\xi[/tex] as a density profile, its small-scale shape should... be fixed in proper coordinates, and its amplitude should scale as [tex](1+z)^{-3}[/tex].... Thus, with [tex]\xi \sim r^{-\gamma}[/tex], we obtain the comoving evolution [tex]\xi(r,z) \sim (1+z)^{\gamma-3}[/tex] (nonlinear).
The [tex]\xi[/tex] I get from the CAMB output does have a fixed small-scale shape, which is consistent with it being in proper coordinates. However, it scales with redshift like [tex](1+z)^{\gamma-3}[/tex], which Peacock describes as "comoving evolution." Does comoving evolution have anything to do with comoving coordinates? If the length scale in CAMB is in comoving coordinates, why does it retain its small-scale shape for different redshifts, like it should in proper coordinates?

Thanks for your help, and sorry if I'm misunderstanding things... I'm very new at this. :P

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