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CAMB: Output the \\psi and \\phi
Posted: March 21 2005
by gongbo zhao
Dear all:
I want to get the \psi and \phi which are the potentials of Newtonian Gauge from CAMB. How can I do that ? Thanks in advance.
Cheers,
Gongbo Zhao
Re: CAMB: Output the psi and phi
Posted: March 21 2005
by Antony Lewis
Equations relating \Psi and \Phi to the synchronous gauge quantities used by CAMB are given in e.g. Eqs. A1,A2,etc of
astro-ph/0212248. Usually it is easiest to use the Poisson equation
[tex]k^2\Phi = \kappa S^2(\delta\rho + 3Hq/k)/2[/tex]
The total matter perturbation ([tex]\kappa S^2\delta\rho[/tex]) and heat fluxe (\kappa\S^2\q) are called
dgrho and
dgq in CAMB's equations.f90. You could write them out in the fderivs or output routine.
Note however that the result for \Phi is numerically unstable on large scales, so if you require an accurate result on large scales (and an analytical one won't do) you may have to evolve the \Phi equation separately. (The early time series solution for \Psi is given in the
notes).
Note also that I have seen every possible different sign convention for both [tex]\Psi[/tex] and [tex]\Phi[/tex]!