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 Large Scale value of $\delta_g/4+2\Phi$
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Joined: 05 Jan 2017
Posts: 7
Affiliation: University of Alberta

 Posted: May 16 2017 Hi, I am plotting the value of δg / 4 + 2Φ from the transfer function output file. If you look at its value at large scales (k = 6.96268e − 06) it's value come out to be ~0.9 rather than the Saachs Wolfe factor of 1 / 5 or 1 / 3. So, I wanted wanted to ask where I am going wrong with my understanding. Thanks, M.J.
Antony Lewis

Joined: 23 Sep 2004
Posts: 1277
Affiliation: University of Sussex

 Posted: May 16 2017 Firstly make sure you are using Newtonian gauge δg not the synchronous gauge one output by default. Secondly there are corrections from neutrino anisotropic stress and recombination not being exactly matter dominated.

Joined: 05 Jan 2017
Posts: 7
Affiliation: University of Alberta

 Posted: May 16 2017 So how can I get the transfer functions in Newtonian gauge or gauges other then synchronous gauge.
Antony Lewis

Joined: 23 Sep 2004
Posts: 1277
Affiliation: University of Sussex

 Posted: May 18 2017 There's no direct way to get that, you'd have to construct the corresponding gauge invariant combination of synchronous gauge density and shear (which you could infer from the output synchronous gauge density, Newtonian-gauge CDM velocity and the Hubble parameter, using relations described in the CAMB notes p22).
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