7-year WMAP data: cosmo implications

[marcus]

http://arXiv.org/abs/1001.4538
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
E. Komatsu, K. M. Smith, J. Dunkley, C. L. Bennett, B. Gold, G. Hinshaw, N. Jarosik, D. Larson, M. R. Nolta, L. Page, D. N. Spergel, M. Halpern, R. S. Hill, A. Kogut, M. Limon, S. S. Meyer, N. Odegard, G. S. Tucker, J. L. Weiland, E. Wollack, E. L. Wright
48 pages, 19 figures. Submitted to Astrophysical Journal Supplement Series
(Submitted on 25 Jan 2010)
"(Abridged) The 7-year WMAP data and improved astrophysical data rigorously tests the standard cosmological model and its extensions. By combining WMAP with the latest distance measurements from the Baryon Acoustic Oscillations (BAO) and the Hubble constant (H0) measurement, we determine the parameters of the simplest LCDM model. The power-law index of the primordial power spectrum is n_s=0.963+-0.012, a measurement that excludes the scale-invariant spectrum by more than 3-sigma. The other parameters, including those beyond the minimal set, are also improved from the 5-year results. Notable examples of improved parameters are the total mass of neutrinos, sum(m_nu)<0.58eV, and the effective number of neutrino species, N_eff=4.34+0.86-0.88, which benefit from better determinations of the third peak and H0. We detect the effect of primordial helium on the temperature power spectrum and provide a new test of big bang nucleosynthesis. We detect, and show on the map for the first time, the tangential and radial polarization patterns around hot and cold spots of temperature fluctuations, an important test of physical processes at z=1090 and the dominance of adiabatic scalar fluctuations. With the 7-year TB power spectrum, the limit on a rotation of the polarization plane due to potential parity-violating effects has improved to Delta(alpha)=-1.1+-1.3(stat)+-1.5(syst) degrees. We report a significant detection of the SZ effect at the locations of known clusters, and show that the current simulations and analytical calculations overestimate the gas pressure, and do not reproduce the observed gas pressure in clusters of galaxies. This result is consistent with the lower-than-expected SZ power spectrum recently measured by the SPT collaboration."

For the whole series of 7-year WMAP reports see:
http://lambda.gsfc.nasa.gov/product/map/dr4/map_bibliography.cfm

 

[clamtrox]

This proves conclusively that Stephen Hawking is god.

(anomalies paper, page 14)

 

[marcus]

Heh heh, some apparently random squiggles in the temperature map resemble the letters S and H, too bad nobody predicted that ahead of time.
The Anomalies paper (Bennett et al) put a box around that patch of the map, to show where the initials are, to make a point about a postiori interpretation.
Thanks for the reference.
If anyone hasn't already seen this, look at Figure 17, on page 14 of http://arXiv.org/abs/1001.4758

 

[marcus]

7-year WMAP leans toward flat infinite LambdaCDM

People can argue about the fine points of interpretation and exactly what words to use in describing the current expert hunches and leanings. The issue certainly is not resolved.

But the Komatsu et al 5-year WMAP paper left more room for the possibility of a positive curved spatial finite LambdaCDM model. It even at one point calculated a lower bound on what the radius of curvature would be---around 100 billion lightyears (now distance, freezing expansion).
That was in Table 2 of WMAP5 Komatsu.

The corresponding WMAP7 paper spends much less time considering that case, and also focuses more on the w=-1 case---the straight LambdaCDM model, no exotic "dark energy", just a simple cosmological constant Lambda.

http://arXiv.org/pdf/1001.4538

There are good reasons for this, I think. As more data accumulates and the errorbounds shrink, the range of uncertainty narrows, it looks increasingly like the simple flat LambdaCDM case.

So they put that up front in their first paragraph.
And they also dropped a little footnote about the 68% confidence interval for Omega_k

The 95% confidence interval they use on page 3, for Table 2 is: -0.0133 < Ω_k < 0.0084

But if you read further, you find on page 18 this footnote:

The 68% CL limit is Ω_k = −0.0023^+0.0054_-0.0056

which translates to -0.0079 < Ω_k < 0.0031

Of course you could say that is LOPSIDED in favor of positive spatial curved, spatial finite universe. But I think the main point is that they are really squeezing the thing down around zero.

For people who are more familiar with the Ω_tot notation, Ω_k is defined to be 1 - Ω_tot. So there is a funny sign-reversal in the notation that you need to be aware of. Negative Ω_k corresponds to positive spatial curvature---the hypersphere picture rather than the infinite flat spatial extent.

So since a lot of us are used to reading Ω_tot = 1 for "flat" I will translate.

The 68% confidence interval says:

0.9969 < Ω_tot < 1.0079

You can see that it has been narrowed down quite a bit since WMAP5 and that it is even more lopsided than it was before, in favor of Omega being slightly bigger than one, which is the spatial finite case.

However the first lesson to take away is that it has narrowed and that the zero curved Omega = 1 point is still in the interval.

 

[ohwilleke]

Most of the WMAP data are doing what physicist thought would be happening at the end of the 19th century, modestly refining physical constants we already had good ball park estimates for, in this case, lambda cold dark matter constants.

The "shocker" of the paper is its suggestion that the WMAP data are more consistent with four or five neutrino generations (with four being more likely than five, but five being more likely than three) than it is with three neutrino generations. Three neutrinos are still within two standard deviations of the expected number of generations based upon the data, however.

The Standard Model, of course, has only three neutrino generations, although adding a fourth generation of fermions to it wouldn't wreck total havoc on the core Standard Model, since the Standard Model doesn't purport to explain why we have the number of fundamental particles or fundamental constants that described them.

But, a significant number of the theories that try to explain the Standard Model's particle zoo and constants from first principles offer up deep reasons (e.g. from symmetry) that there must be exactly three generations of fermions.

Since WMAP is such gold standard data, a result at odds with the standard model drawn from it has more credibility than the usual "here's another Beyond The Standard Model theory" preprint. Since WMAP is generally consistent with prior observations of cosmic background radiation, and involves a one of a kind phenomena, it is also data that won't be refuted in further experiments. One can rethink the theory used to derive the conclusion reached, but the data aren't going to change materially.

On the other hand, new results of the MINOS collaboration at Fermilab (http://www.symmetrymagazine.org/breaking/2010/02/02/new-minos-results-%e2%80%9cstrongly-disfavor%e2%80%9d-sterile-neutrino-neutrino-decay/ ) disfavor a fourth generation neutrino, at least if it fits the profile of a "sterile neutrino."

The math that is being used to make the WMAP conclusion is also not purely "ex post" theorizing. There was published work on this kind of analysis in 1999 in JETP Letters
( http://www.springerlink.com/content/v34lxuh37727r3p4/ ) (and probably elsewhere as well), before WMAP data was available to prove it. This was analyzed, ex post, with the five year WMAP data ( http://en.wikipedia.org/wiki/Neutrino#Mass ).

 

[clamtrox]

Improvement in Omega_K comes mostly from the better supernova data they are using.

 

[cepheid]

The corresponding WMAP7 paper spends much less time considering that case, and also focuses more on the w=-1 case---the straight LambdaCDM model, no exotic "dark energy", just a simple cosmological constant Lambda.

Hi marcus,

I just wanted to ask you if you could clarify what you meant here. I thought that "dark energy" was the prevailing interpretation of the effects of the cosmological constant (i.e. physical "explanation" for them), and that taking w = -1 just means saying that this dark energy has a particularly simple equation of state: p = -ϱc². It sounded kind of like you were saying that w = -1 excludes dark energy altogether as an explanation for the cosmological constant (in favour of...?). This could be more a case of semantics/terminology, and again, it is not my intention to nitpick your wording or criticize you, I just wanted clarification on what you were saying, because I'm sure you have much more insight into Λ than I do as well as a better handle on what the standard terminology in the field is.

By the way, thanks so much for summarizing the key results of the paper so neatly!

 

[marcus]

Yeah, my wording wasn't clear. I meant no exotic dark energy. I think of the cosmological constant form of dark energy, with w = 1, as somehow normal. It is familiar and ordinary dark energy---what I naturally think of in connection with dark energy.

If dark energy is NOT associated with a simple cosmological constant then I think of it as exotic---strange weird. Maybe it is not constant, maybe the energy density is changing with time. Or maybe the equation of state w is changing with time. Something weird.

I need some word for non-normal dark energy. Do you think "exotic" works? Can you suggest an alternative?

Should I say "abnormal w≠1 dark energy"?

Anyway, do you understand what I was trying to say?

 

[cepheid]

Yeah, my wording wasn't clear. I meant no exotic dark energy. I think of the cosmological constant form of dark energy, with w = 1, as somehow normal. It is familiar and ordinary dark energy---what I naturally think of in connection with dark energy.

Gotcha

I need some word for non-normal dark energy. Do you think "exotic" works?

Sure?

Can you suggest an alternative?

I don't have any ideas...

Anyway, do you understand what I was trying to say?

Yup!

 

[Ich]

I need some word for non-normal dark energy.

I think Quintessence is close. Or the fifth elephant.

 

[edpell]

Anyway, do you understand what I was trying to say?

Marcus, thanks for point out this very good paper to us.

Am I correct in understanding that the idea of inflation in the early (<<1second) universe leads us to expect a universe close to flat?

 

[marcus]

Marcus, thanks for point out this very good paper to us.

Am I correct in understanding that the idea of inflation in the early (<<1second) universe leads us to expect a universe close to flat?

You are most welcome! I hope more people will take a look at the WMAP7 results.

That is correct about inflation. The observation that the universe is nearly flat has become one of the strongest motivations for assuming some kind of inflation occurred.

You probably know the main arguments for inflation

1. observed flatness or near flatness
2. observed background temperature near uniformity (nearly same temperature in all directions)
3. observed scale invariance of fluctuations in the background temperature map (intuitively, as much narrow-angle fluctuation as wide-angle, as much variation in the little bumps as in the big blotches)---a feature of the angular power spectrum.

It is hard to think of some early universe process besides inflation that would cause those things. Inflation itself is not so attractive because it requires some exotic field, some never-yet-observed "dark-energy-on-steroids" which causes terrific expansion and then abruptly decays. It is very contrived. No model of physics predicts an energy field like that. The reason inflation is widely accepted is because nobody can think of an attractive simple alternative that would account for things like 1. 2. and 3.

There are other scenarios but they aren't so popular because they are even more weird and exotic, or they don't do as good a job explaining, or they explain only one or two of the oddities but not the third, and so on.

I suspect that's familiar ground for you. In any case definitely YES. Inflation, if you buy it, will explain the observed flatness or near-flatness.

=========
4. I forgot another thing that inflation helps explain---we don't observe magnetic monopoles. A bunch may have been created near the start of expansion but then inflation "diluted" them by creating this huge volume of space. Explains why they are so rare that they seem not to exist. (For some reason this justification of inflation is one I don't hear about much any more, maybe the first 3 reasons are more obvious.)