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 CAMB: Lensing potential power spectrum
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Sudeep Das

Joined: 13 Dec 2005
Posts: 2
Affiliation: Princeton University

 Posted: December 12 2006 Does the Lensing potential power spectrum $C_l^{\phi}$ that CAMB churns out include nonlinear corrections from halofit?
Antony Lewis

Joined: 23 Sep 2004
Posts: 675
Affiliation: University of Sussex

 Posted: December 12 2006 Not by default, but you can set do_nonlinear = 2 in the .ini file to add corrections.
Sudeep Das

Joined: 13 Dec 2005
Posts: 2
Affiliation: Princeton University

Posted: March 01 2007

 Antony Lewis wrote: Not by default, but you can set do_nonlinear = 2 in the .ini file to add corrections.

Hi Antony,
When I plot $\ell^4 C_\ell^{\phi\phi}$ vs. $\ell$ with do_nonlinear=0 and do_nonlinear=2 I get almost identical plots:

When I do my own Limber approximation based calculation using the power spectrum from CAMB I get the non-linear potential power spectra to be appreciably higher than the linear case for high l's. I think that should be the case. Am I missing something here?
Antony Lewis

Joined: 23 Sep 2004
Posts: 675
Affiliation: University of Sussex

 Posted: March 01 2007 Probably not using high enough k_eta_max_scalar ? (note CMB lensing for non-BB is insensitive to the high l part of the lensing potential power spectrum; you need k_eta_max_scalar much higher to get the lensing potential accurately than you do to get the lensed Cl accurately)
Gabriela Calistro Rivera

Joined: 15 Aug 2011
Posts: 1
Affiliation: Heidelberg University

 Posted: August 15 2011 Hello, I'm simulating the lensed CMB in a similar way as Lenspix for my Bachelor Thesis. Using the HEALPix routine synfast I have calculated the gradient of the lensing potential given by CAMB and as next the Cldd of the absolute value of the deflection angle. In the ReadMe file of CAMB, they say Cldd= [l(l+1)]2 /(2π) ClΦΦ, where the Cldd given as output here is equivalent to (l(l+1)) /(2π) * Cl(computed)dd , which is my computed deflection angle power spectrum, right?. But if I plotting this relation, I get a great difference between both! (uploaded figure plot4.eps). I don't understand the problem, since it seems that my results of the deflection angles are right (going on with the remapping, the produced lensed temperature power spectra fits very well with the theoretical of CAMB). I wonder if I have a false interpretation of the information given in the ReadMe? Thanks for the help in anticipation! Gabriela
Antony Lewis

Joined: 23 Sep 2004
Posts: 675
Affiliation: University of Sussex

 Posted: August 17 2011 "absolute value of the deflection angle"? You don't want $|\nabla\psi|$, but the power spectrum of the gradient (E)-mode part of spin−1 harmonic transform of the map of $\nabla\psi$ (see e.g. appendix of astro-ph/0502469)
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