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### Large Scale value of $\\delta_g/4+2\\Phi$

Posted: **May 16 2017**

by **Muhammad Junaid**

Hi, I am plotting the value of [tex]\delta_g/4+2\Phi[/tex] from the transfer function output file. If you look at its value at large scales ([tex]k=6.96268e-06[/tex]) it's value come out to be ~[tex]0.9[/tex] rather than the Saachs Wolfe factor of [tex]1/5[/tex] or [tex]1/3[/tex]. So, I wanted wanted to ask where I am going wrong with my understanding.

Thanks,

M.J.

### Re: Large Scale value of $\\\\delta_g/4+2\\\\Phi$

Posted: **May 16 2017**

by **Antony Lewis**

Firstly make sure you are using Newtonian gauge [tex]\delta g[/tex] not the synchronous gauge one output by default. Secondly there are corrections from neutrino anisotropic stress and recombination not being exactly matter dominated.

### Large Scale value of $\\delta_g/4+2\\Phi$

Posted: **May 16 2017**

by **Muhammad Junaid**

So how can I get the transfer functions in Newtonian gauge or gauges other then synchronous gauge.

### Re: Large Scale value of $\\\\delta_g/4+2\\\\Phi$

Posted: **May 18 2017**

by **Antony Lewis**

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).