[Cosmo-torun] cosmo workshop Fri 15:00 12.03.2010: Li and Liu arXiv:1003.1073: WMAP quadrupole = antenna direction interpolation error
boud w astro.uni.torun.pl
Pią, 12 Mar 2010, 09:27:52 CET
This is being discussed on cosmocoffee as well:
Liu is participating in the discussion. He contacted Hinshaw
but yesterday said that he had not yet received a reply.
The software for analysing the TOD is also linked in the
Looking forward to this afternoon's discussion, :)
On Mon, 8 Mar 2010, Boud Roukema wrote:
> witam cosmo-torun
> Cosmo workshop
> WHEN: Fri 15:00 12.03.2010
> WHO: boud
> TITLE: Liu and Li arXiv:1003.1073 ("The origin of the WMAP quadrupole")
> ABSTRACT: The WMAP quadrupole is apparently
> mostly a pointing error. The true quadrupole is much
> closer to zero. The missing fluctuations problem has
> just got much worse for the infinite-flat-universe hypothesis.
> Liu and Li arXiv:1003.1073 ("The origin of the WMAP quadrupole") have
> posted a very interesting article (presumably submitted to Nature,
> guessing from the style and length). The best estimate of the CMB
> quadrupole is apparently... zero!
> They claim that the WMAP quadrupole comes from a single error - an
> antenna direction representation error by half of an observational
> angular interval. The discussion concerns quaternions, but don't
> be frightened - it presumably uses the imaginary part only, to
> represent X, Y, Z directions. You can think of them as vectors
> in R^3 if you like.
> Order of magnitude check of their calculation:
> Liu and Li say that the error is by 7' and that this causes
> incorrect subtraction of the dipole in the time-ordered-date (TOD).
> The direction of the error varies as the direction of observation
> varies, so it's reasonable that it doesn't give a simple offset
> detectable by post-processing in the analysis pipeline, IMHO
> (though Bartek may have another opinion).
> The dipole is about 3.3mK (e.g. section 7 Bennett et al 2003).
> sin(7') * 3.3mK = 0.002 * 3.3mK = 6.7 microK
> Liu and Li say 10-20 microK, just slightly higher, but their Eq.(1)
> is a motivational equation - it is not used as an entry to
> their data analysis pipeline.
> Figures 1 and 2 should the effect very dramatically. Rephrasing what
> they've said:
> Figure 1 left: difference between Liu Li analysis, using the same wrong
> method that the WMAP team used. This is a check that their pipeline
> does the same thing that the WMAP team does. |Difference| < 2 or so microK.
> Figure 1 right: Liu Li using correct antenna directions on WMAP Q1 3yr data.
> They get a strong quadrupole!
> Figure 2 left: The effect of using a wrong dipole, calculated using *only the
> directional information* from the time-ordered-data from the spacecraft,
> with *no CMB data*. See paragraph 2, page 4: "only the spacecraft attitude
> information is used to compute d' ."
> Figure 2 right: official WMAP5 V+W quadrupole.
> Figures 1 right, and 2 left look very, very similar to Figure 2 right.
> There seems to be a slight difference in angular position visible by eye,
> but the coincidence is striking.
> Can we really believe that the CMB quadrupole just by chance happens to be very
> strongly aligned with and of nearly identical amplitude to a map made
> using only the time-ordered-data of the spacecraft direction
> ("attitude") and the spacecraft orbit around the Sun, and the Sun's
> motion with respect to the CMB?
> Since this is a Nature-type article, the authors are forced to exclude almost
> all interesting details from the article, but info like the spacecraft
> attitude quaternions and interpolation method should not be too difficult to
> * Bennett et al 2003: arXiv:astro-ph/0302207
> * Liu, Li 2010: arXiv:1003.1073
> The good thing about this is that it shows that a lot of very
> intelligent people - those in a mega-collaboration plus many outside
> of the official group - can spend 7 years looking closely at an
> important set of observational data without finding what appears to be
> a very elementary error in the analysis details, with a very
> fundamental consequence.
> The fundamental consequence is that a lower quadrupole makes Infeld's
> (1949) prediction of the equivalent of the low l cutoff due to the
> shape of the Universe even stronger! Liu & Li suggest an inflationary
> argument, but their interpretation is not what is important - they
> don't want the referee to make a fuss about interpretations, since
> their observational argument is so strong.
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