CosmoCoffee

[Antony Lewis]

Would cover

1. Small shift on WMAP2 error bars due to lensed power spectrum
2. Discussion of n_s-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?

[Antony Lewis]

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

[The simulation input model had n_s = 0.99, A_s = 2.5×10 ^{- 9}, Ω_bh² = 0.022, Ω_bh² = 0.12, τ = 0.15 and h = 0.72].