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March 16, 2006

WMAP Results

WMAP has released their 2nd and 3rd year data.

The measurements of the CMBR anisotropy show clear signs of the 3rd acoustic peak.

WMAP 3rd year CMBR power spectrum WMAP CMBR power spectrum, for multipole moments, l=2,...,1000l=2,...,1000.

On the subject of polarization, they find no evidence for BB-modes and an upper limit on the scalar/tensor ratio, r=0.55r=\lesssim 0.55, which is getting close to the predictions of simple inflationary models, r0.3r\sim 0.3.

The fit to the ΛCDM model has improved markedly over the first year results.

Best fit for Cosmological Parameters from WMAP Year 3
100Ω bh 2100\Omega_b h^2 2.233+0.072 0.0912.233\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.072\\ -0.091}}\right. 2.203+0.072 0.0902.203\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.072\\ -0.090}}\right. 2.228+0.066 0.0822.228\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.066\\ -0.082}}\right. 2.223+0.066 0.0832.223\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.066\\ -0.083}}\right.
Ω mh 2\Omega_m h^2 0.1268+0.0073 0.01280.1268\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.0073\\ -0.0128}}\right. 0.1238+0.0066 0.01180.1238\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.0066\\ -0.0118}}\right. 0.1271+0.0070 0.01280.1271\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.0070\\ -0.0128}}\right. 0.1262+0.0050 0.01030.1262\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.0050\\ -0.0103}}\right.
hh 0.734+0.028 0.0380.734\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.028\\ -0.038}}\right. 0.738+0.028 0.0370.738\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.028\\ -0.037}}\right. 0.733+0.030 0.0380.733\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.030\\ -0.038}}\right. 0.732+0.018 0.0250.732\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.018\\ -0.025}}\right.
AA 0.801+0.043 0.0540.801\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.043\\ -0.054}}\right. 0.798+0.047 0.0570.798\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.047\\ -0.057}}\right. 0.801+0.048 0.0560.801\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.048\\ -0.056}}\right. 0.799+0.042 0.0510.799\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.042\\ -0.051}}\right.
τ\tau 0.088+0.028 0.0340.088\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.028\\ -0.034}}\right. 0.084+0.031 0.0380.084\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.031\\ -0.038}}\right. 0.084+0.027 0.0340.084\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.027\\ -0.034}}\right. 0.083+0.027 0.0310.083\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.027\\ -0.031}}\right.
n sn_s 0.951+0.015 0.0190.951\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.015\\ -0.019}}\right. 0.945+0.015 0.0190.945\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.015\\ -0.019}}\right. 0.949+0.015 0.0190.949\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.015\\ -0.019}}\right. 0.948+0.014 0.0180.948\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.014\\ -0.018}}\right.
σ 8\sigma_8 0.744+0.050 0.0600.744\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.050\\ -0.060}}\right. 0.722+0.044 0.0560.722\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.044\\ -0.056}}\right. 0.742+0.045 0.0570.742\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.045\\ -0.057}}\right. 0.737+0.033 0.0450.737\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.033\\ -0.045}}\right.
Ω m\Omega_m 0.238+0.027 0.0450.238\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.027\\ -0.045}}\right. 0.229+0.026 0.0420.229\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.026\\ -0.042}}\right. 0.239+0.025 0.0460.239\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.025\\ -0.046}}\right. 0.236+0.016 0.0290.236\left.\scriptsize{\array{\arrayopts{\align{center}\colalign{left}} +0.016\\ -0.029}}\right.
  • Ω b=\Omega_b= (fractional) energy density in baryons
  • Ω m=\Omega_m= (fractional) energy density in matter =Ω b+Ω ν+Ω CDM=\Omega_b+\Omega_\nu +\Omega_{CDM}
  • n s=n_s= spectral density of scalar fluctuations
  • h=H 0/(100km/s/Mpc)h=H_0/(100 km/s/Mpc)
  • A=A= amplitude of density fluctuations (k=0.002k = 0.002/Mpc)
  • τ=\tau= reionization optical depth
  • σ 8=\sigma_8= linear theory amplitude of matter fluctuations at 8h 18h^{-1} Mpc

The full list of papers, doubtless contains more nuggets of information. Perhaps our cosmologist friends over at CosmicVariance will provide some insight.


More from Sean Carroll and Steinn Sigurðsson (I,II).
Posted by distler at March 16, 2006 1:44 PM

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Re: WMAP Results


Just a heads-up: The WMAP Power Spectrum picture (the first one on your post) does not seem to be showing… and, in fact, if you try to actually open the image file, it complains that the file does not exist.


Posted by: Daniel Doro Ferrante on March 16, 2006 3:14 PM | Permalink | Reply to this

Re: WMAP Results

Would the low value for the quadrupole l=2 really indicate a non-trivial topology (as I read somewhere else) or are there other explanations?

Posted by: wolfgang on March 16, 2006 9:48 PM | Permalink | Reply to this


That explanation is hard to reconcile with the data.

More importantly, the observation of the very low ll modes is inherently limited by cosmic variance. You can’t ever measure the quadrupole well enough to say definitively that there is a problem.

Posted by: Jacques Distler on March 16, 2006 10:01 PM | Permalink | PGP Sig | Reply to this

Re: WMAP Results

What parameters, including constants, would you use to make the data oscillations fit the theoretical at high and low l? Changing the speed of light might not matter, but maybe both the speed of light and gravity might work to 3% or so at high and low l, in altering the cross sections, also in big bang nucleosynthesis. Perhaps string theory is also required to explain the data more accurately?

Posted by: anonymous on March 19, 2006 5:50 PM | Permalink | Reply to this

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