[astro-ph/0507503] Cosmological Parameters from the 2003 flight of BOOMERANG

Authors:  C. J. MacTavish, P. A. R. Ade, J. J. Bock, J. R. Bond, J. Borrill, A. Boscaleri, P. Cabella, C. R. Contaldi, B. P. Crill, P. de Bernardis, G. De Gasperis, A. de Oliveira-Costa, G. De Troia, G. Di Stefano, E. Hivon, A. H. Jaffe, W. C. Jones
Abstract:  We present the cosmological parameters from the CMB intensity and polarization power spectra of the 2003 Antarctic flight of the BOOMERANG telescope. The BOOMERANG data alone constrains the parameters of the $\Lambda$CDM model remarkably well and is consistent with constraints from a multi-experiment combined CMB data set. We add LSS data from the 2dF and SDSS redshift surveys to the combined CMB data set and test several extensions to the standard model including: running of the spectral index, curvature, tensor modes, the effect of massive neutrinos, and an effective equation of state for dark energy. We also include an analysis of constraints to a model which allows a CDM isocurvature admixture.
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Anze Slosar
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[astro-ph/0507503] Cosmological Parameters from the 2003 fli

Post by Anze Slosar » July 26 2005

I finally got some time to read this very carefuly written parameter-estimation paper (very much Antony Lewis' child, seems to me). It shows how very difficult is to make any serious progress in the field, these days.
Anyway, my questions:
  • This cross-calibration bussiness: B03 is cross-calibrated to WMAP, so the calibration between the two is better than the B03 2% absolute calibration. Has this been taken into account? Surely it must improve things the depend on ratio of high-l power to low-l power (say tau?)
  • This cutting low multipoles bussiness: Ok, I agree that data-sets are cosmic variance coupled to the WMAP, which is cosmic variance limited to 350, so must cut everything else below 350.... But the default cosmomc datasets for VSA and CBI and others are still cut at 600?
  • This neutrino mass bussiness: I think that this looks quite exciting and we are already beating beta decay experiments black and blue. Now, how much do people believe the hard-core limits of m_\nu<0.16. To get this we need all CMB + LSS + b_g=1 .0 \pm 0.1. I am quite happy to buy this, and I do believe the bispectrum measurements of b_g. Do others buy this as well?

William Jones
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Re: [astro-ph/0507503] Cosmological Parameters from the 2003

Post by William Jones » July 27 2005

Anze Slosar wrote:
  • This cross-calibration bussiness: B03 is cross-calibrated to WMAP, so the calibration between the two is better than the B03 2% absolute calibration. Has this been taken into account? Surely it must improve things the depend on ratio of high-l power to low-l power (say tau?)
The B03 calibration uncertainty is limited by the (relatively low) signal to noise in the WMAP maps. Therefore the calibration between the two is not much better since the uncertainty on the absolute calibration of WMAP is fairly small. That is, if WMAP had no calibration uncertainty, the B03 uncertainty would be roughly sqrt(.02^2 - 0.008^2) instead of .02, making little difference in the marginalization.

William Jones
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Re: [astro-ph/0507503] Cosmological Parameters from the 2003

Post by William Jones » July 27 2005

Anze Slosar wrote: [*] This cutting low multipoles bussiness: Ok, I agree that data-sets are cosmic variance coupled to the WMAP, which is cosmic variance limited to 350, so must cut everything else below 350.... But the default cosmomc datasets for VSA and CBI and others are still cut at 600?
The B03 window functions allow a binning \Delta \ell \sim 50 (100) for the temperature (polarization) data, whereas those of the interferometers are much larger. For example, the first published CBI bin extends from 0<\ell<600. All one can do, given the data, is drop the first bin. Granted, the window functions of the temperature data from the CBI mosaic and VSA observations are more comparable to B03, but in any case they don't contribute much statistical weight to WMAP/B03 at those multipoles.

Antony Lewis
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Re: [astro-ph/0507503] Cosmological Parameters from the 2003

Post by Antony Lewis » July 27 2005

Anze Slosar wrote: This cutting low multipoles bussiness: Ok, I agree that data-sets are cosmic variance coupled to the WMAP, which is cosmic variance limited to 350, so must cut everything else below 350.... But the default cosmomc datasets for VSA and CBI and others are still cut at 600?
The B03 analysis does not use the same cuts for the other datasets as supplied by default with CosmoMC.

Ideally of course you would include all the data and correctly account for the correlation between datasets. Otherwise where to cut is perhaps a matter of taste: e.g. if you think WMAP is more reliable than say VSA on the scales of overlap then it makes sense to cut at higher l. 600 is around where error bars from WMAP become worse than from other sets and correlation errors should be negligible, though cutting at lower l should be nearly valid. In practice I think it usually makes very little difference.

(btw, Carrie MacTavish did most of the stuff for this paper - not me.. I just made a few cosmomc changes and helped out a bit)

Anze Slosar
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Re: [astro-ph/0507503] Cosmological Parameters from the 2003

Post by Anze Slosar » July 27 2005

Antony Lewis wrote: In practice I think it usually makes very little difference.
Yep, I agree it is mostly an academical question: WMAP is so strong other datasets pretty much just add a constant offset in \chi^2 at multipoles of overlap...
Antony Lewis wrote: (btw, Carrie MacTavish did most of the stuff for this paper - not me.. I just made a few cosmomc changes and helped out a bit)
Oops, I apologise for the misattribution.

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