## CAMB : Weyl potential

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Stéphane Ilic
Posts: 17
Joined: February 11 2014
Affiliation: IRAP Toulouse

### CAMB : Weyl potential

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 ($\Phi=(\phi+\psi)/2$ 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 $T_{\Phi}(k)$ the content of column 10 of the "transfer_out" file, am I mistaken to say that the power spectrum I'm looking for is $P_{\Phi}(k) = P_{\chi}(k) T_{\Phi}(k)^2$, with $P_{\chi}(k)$ being the primordial spectrum $P_{\chi}(k)=A_s (k/k_{pivot})^{n_s-1}$ ?

Thanks a lot in advance !

S.

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

### Re: CAMB : Weyl potential

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

A quick question though : in the "transfer_out" file, the various transfer functions are actually divided by $k^2$ : is it also the case for the Weyl potential ?

S.

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

### Re: CAMB : Weyl potential

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

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 $k^2$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

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