Wilkinson Microwave Anisotropy Probe (WMAP) three year results: implications for cosmology
Summary (2 min read)
1. INTRODUCTION
- The power-law CDM model fits not only the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data, but also a wide range of astronomical data (Bennett et al. 2003; Spergel et al. 2003).
- The primordial fluctuations in this model are adiabatic, nearly scaleinvariant Gaussian random fluctuations (Komatsu et al. 2003).
2. METHODOLOGY
- The basic approach of this paper is similar to that of the firstyear WMAP analysis: their goal is to find the simplest model that fits the CMB and large-scale structure data.
- While these models have somewhat higher amplitudes than the new best-fit WMAP values, a recent analysis by Desjacques & Nusser (2005) find that theLy data are consistentwith 8 between 0.7 and 0.9.
- Recent analyses of both optical and X-ray cluster samples yield cosmological parameters consistent with the best-fitWMAP CDMmodel (Borgani et al.
- The lensing data are most discrepant and it most strongly pulls the combined results toward higher amplitudes and higher m (see Figs. 7 and 9).
5. CONSTRAINING THE SHAPE OF THE PRIMORDIAL POWER SPECTRUM
- While the simplest inflationary models predict that the spectral index varies slowly with scale, inflationary models can produce strong scale-dependent fluctuations (see e.g., Kawasaki et al.
- Small-scale CMB measurements (Readhead et al. 2004a) also favor running spectral index models over power-law models.
- As in the Martin & Ringeval model, the improvements in the 2eA are driven by improvements in the fit around l 30Y100 and the first peak.
- Simple inflationary models predict that the slope of the primordial power spectrum, ns, differs from 1 and also predict the existence of a nearly scale-invariant spectrum of gravitational waves.
- The authors compare the simplest inflationary models to the WMAP 3 year data and to other cosmological data sets.
OF THE UNIVERSE
- Over the past two decades, there has been growing evidence for the existence of dark energy (Peebles 1984; Turner et al.
- The pair offigures show that CMB data can place strong limits on models withw < 1 and nonclustering dark energy.
- The limits on neutrinomasses fromWMAP data alone are now very close to limits based on combined CMB data sets.
- The combination of WMAP data and other astronomical data places strong constraints on the geometry of the universe (see Table 12): 1. The angular scale of the baryon acoustic oscillation (BAO) peak in the SDSS LRG sample (Eisenstein et al. 2005) measures the distance to z ¼ 0:35.
8. ARE CMB FLUCTUATIONS GAUSSIAN?
- The detection of primordial non-Gaussian fluctuations in the CMBwould have a profound impact on their understanding of the physics of the early universe.
- While the simplest inflationary models predict only mild non-Gaussianities that should be undetectable in theWMAP data, there are a wide range of plausible mechanisms for generating significant and detectable non-Gaussian fluctuations (see Bartolo et al. 2004a for a recent review).
- Several different groups (Gaztañaga &Wagg 2003; Mukherjee &Wang 2003; Cabella et al. 2004; Phillips & Kogut 2006; Creminelli et al. 2006) have applied alternative techniques to measure fNL from the maps and have similar limits on fNL.
- Since the release of theWMAP data, several groups have claimed detections of significant non-Gaussianities (Tegmark et al.
- 2. Size and Shape of Hot and Cold Spots Minkowski functionals (Minkowski 1903; Gott et al.
9. CONCLUSIONS
- The standard model of cosmology has survived another rigorous set of tests.
- The combination of WMAP measurements and other astronomical measurements place significant limits on the geometry of the universe, the nature of dark energy, and even neutrino properties.
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Frequently Asked Questions (12)
Q2. What are the constraints on the amplitude of the Bmode signal?
Since the authors are constraining models with tensor modes, the authors also use theWMAP constraints on the amplitude of the Bmode signal in the analysis.
Q3. What is the effect of the CMB data on the amplitude of matter fluctuations?
The presence of a significant neutrino component lowers the amplitude of matter fluctuations on small scales, by roughly a factor proportional to ( P m ), where P m is the total mass summed over neutrino species, rather than the mass of individual neutrino species.
Q4. What is the biggest source of uncertainty in the CMB predictions?
Prior to the measurements of the CMB power spectrum, uncertainties in the baryon abundance were the biggest source of uncertainty in CMB predictions.
Q5. What are the common models with weak parameter degeneracies?
more general models, most notably thosewith nonflat cosmologies andwith richer dark energy or matter content, have strong parameter degeneracies.
Q6. What are the parameters that are terrible fits to the data?
the parameters fitted to the nocosmological-constant model, (H0 ¼ 30 km s 1 Mpc 1 andm ¼ 1:3) are terrible fits to a host of astronomical data: largescale structure observations, supernova data, and measurements of local dynamics.
Q7. Where did Hinshaw and Page (2007) describe their approach to addressing this concern?
Hinshaw et al. (2007) and Page et al. (2007) describe their approach to addressing this concern: for lowmultipoles, the authors explicitly compute the likelihood function for the WMAP temperature and polarization maps.
Q8. How much has the error in the high-l temperature multipoles decreased?
With longer integration times and smaller pixels, the errors in thehigh-l temperature multipoles have shrunk by more than a factor of 3.
Q9. What are the improvements in the analysis of high-l temperature data?
There are several improvements in their analysis of high-l temperature data (Hinshaw et al. 2007): better beam models, improved foreground models, and the use of maps with smaller pixels (Nside ¼ 1024).
Q10. What is the effect of the neutrino species on the angular power spectrum?
In addition, the presence of these additional neutrino species alters the damping tail and leaves a distinctive signature on the high-l angular power spectrum (Bashinsky & Seljak 2004) and on the small-scale matter power spectrum.
Q11. What is the effect of the source correction on the best-fit slope?
The detailed form of the likelihood function and the treatment of point sources and the SZ effect has a 0.5 effect on the best-fit slope.
Q12. How can the authors constrain k and w?
Figure 15 shows that by using the combination of CMB, large-scale structure, and supernova data, the authors can simultaneously constrain both k and w.