CAMB : Weyl potential

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Stéphane Ilic
Posts: 17
Joined: February 11 2014
Affiliation: IRAP Toulouse

CAMB : Weyl potential

Post by Stéphane Ilic » November 22 2015

Hello everyone,

I am trying to do some calculations in the context of lensing and the ISW effect, and to do so, I need the power spectrum of the Weyl potential ([tex]\Phi=(\phi+\psi)/2[/tex] as defined in CAMB). If I understand well, CAMB can output something close to this among all the other transfer functions. More precisely, if I call [tex]T_{\Phi}(k)[/tex] the content of column 10 of the "transfer_out" file, am I mistaken to say that the power spectrum I'm looking for is [tex]P_{\Phi}(k) = P_{\chi}(k) T_{\Phi}(k)^2[/tex], with [tex]P_{\chi}(k)[/tex] being the primordial spectrum [tex]P_{\chi}(k)=A_s (k/k_{pivot})^{n_s-1}[/tex] ?

Thanks a lot in advance !

S.

Antony Lewis
Posts: 1547
Joined: September 23 2004
Affiliation: University of Sussex
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Re: CAMB : Weyl potential

Post by Antony Lewis » November 22 2015

Looks right to me. [where k and k/h are interpreted consistently]

Stéphane Ilic
Posts: 17
Joined: February 11 2014
Affiliation: IRAP Toulouse

CAMB : Weyl potential

Post by Stéphane Ilic » November 22 2015

Thanks for your reply Antony !
A quick question though : in the "transfer_out" file, the various transfer functions are actually divided by [tex]k^2[/tex] : is it also the case for the Weyl potential ?
Thanks in advance !

S.

Antony Lewis
Posts: 1547
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: CAMB : Weyl potential

Post by Antony Lewis » November 23 2015

No (as far as I remember and according to the readme)

Stéphane Ilic
Posts: 17
Joined: February 11 2014
Affiliation: IRAP Toulouse

CAMB : Weyl potential

Post by Stéphane Ilic » November 23 2015

Thanks again Antony ! One last thing : I just checked the source code a few moments ago, and I noticed the following comment in the "equations.f90" file : "Transfer_Weyl is [tex]k^2[/tex]Phi, where Phi is the Weyl potential", where "Transfer_Weyl" is what is actually outputted in column 10 of the "transfer_out" file.

Do you remember what that comment means exactly ? Is it relevant to my initial question ?

Cheers !

S.

Antony Lewis
Posts: 1547
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: CAMB : Weyl potential

Post by Antony Lewis » November 23 2015

Just that k^2 factor is included here so that when divided by k^2 later it comes out as being just Weyl.

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