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Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

CMB lensing and effect on parameters
 
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1270
Affiliation: University of Sussex

PostPosted: September 23 2004  Reply with quote

Would cover

1. Small shift on WMAP2 error bars due to lensed power spectrum
2. Discussion of ns-A-tau-ombh2 degeneracy with lensing (made worse)
3. Test mock Planck data to see if power spectrum analysis is sufficient or whether non-Gaussianities need to be fully modelled
4. Effect of lensing on Planck forecasts

Would include documentation of LensPix simulation code.

Any overlaps with other work/suggestions?
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1270
Affiliation: University of Sussex

PostPosted: December 06 2004  Reply with quote

I'm not sure when I'm going to get round to writing up the conclusions of this. Here's a summary.

Using the lensed Cl seems to work fine for parameter estimation as long as you compute the theoretical result accurately. In particular the 2nd-order perturbative result (e.g. astro-ph/0001303) is not accurate enough. Here's a comparison with the correct result



Red is the 2nd order result, and biases parameters for Planck. The blue result is that of astro-ph/9505109, which is actually pretty much accurate enough for Planck. The very accurate 'correct' result was generated using the Nov 2004 version of CAMB using a new full-sky generalization of the result in astro-ph/9505109 (work with Anthony Challinor).

Using the accurate Cl calculation, for a typical idealized Planck-like simulation I get parameter constraints for a vanilla model like this:



Here black is analysing the lensed sky with the lensed Cl, red is analysing the unlensed sky with the unlensed Cl, and blue is the wrong result if you analyse the lensed sky but neglect lensing in the Cl calculation. The lensed results neglects non-gaussianity of the lensed field.

[The simulation input model had ns = 0.99, As = 2.5×10 - 9, Ωbh2 = 0.022, Ωbh2 = 0.12, τ = 0.15 and h = 0.72].
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