1 / 16

Cosmological Parameters and the WMAP data

Cosmological Parameters and the WMAP data. Antony Lewis CfA, Harvard / CITA, Toronto http://cosmologist.info. Standard assumptions – what are the parameters? Unexpected features, validity of assumptions? Low quadrupole, cut-off/running/dark energy Asymmetries

gustavob
Download Presentation

Cosmological Parameters and the WMAP data

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cosmological Parameters and the WMAP data Antony Lewis CfA, Harvard / CITA, Toronto http://cosmologist.info • Standard assumptions – what are the parameters? • Unexpected features, validity of assumptions? • Low quadrupole, cut-off/running/dark energy • Asymmetries • ‘features’ of WMAP analysis

  2. MCMC sampling for parameter estimation • MCMC sample points in cosmological parameter space drawn from the posterior distribution given the data P(parameters|data) • Each sample gives an equally likely set of parameters given the data. “possible universes” • Number density of samples proportional to probability density • Just requires a function to compute likelihood for each set of parameters • CosmoMC code at http://cosmologist.info/cosmomcuses CAMB (http://camb.info) to generate Cl • Lewis, Bridle: astro-ph/0205436

  3. Cosmological Parameters:combining CMB+Weak Lensing WMAP+ACBAR+CBI+VSA with RCS + weak BBN prior Contaldi, Hoekstra, Lewis: astro-ph/0302435

  4. Vanilla Universe marginalized parameter constraints flat, massless neutrinos, cosmological constant, power law power spectrum, … large compared to WMAPext+2dF (0.134±0.006) Good agreement with more conservative independent CMB+2dF analysis

  5. WMAP TT power spectrum at low l compared to theoretical power law model (mean over realizations) Pseudo-Cl data points from http://lambda.gsfc.nasa.gov/

  6. Likelihood of theoretical value given observed value Observed Standard models Low quadrupole? WMAP Pseudo-Cl: C2 = 123 Tegmark cleaned map: C2 = 184 (kp2 cut, Pseudo-Cl estimator on map from astro-ph/0302496) Foreground uncertainty: Likelihood modelling:

  7. Running ns? WMAP+CMB+2dF, with and without l =2,3,4 multipoles Low quadrupole and octopole drive ~1 sigma evidence for running Need small scale data more reliable than Lyman-α

  8. Cut-off in initial power spectrum? Bridle, Lewis, Weller, Efstathiou: astro-ph/0302306 P(k)=0 for k<kc ~ 3 x 10-4Mpc-1Slightly favoured by the dataDoes not give very low quadrupolebecause of ISW contribution from larger k>kc

  9. Total ISW Δk Last scattering k MPc Contributions to the quadrupole

  10. Changing ISW is tricky… E.g. Dark energy with w > -1,cs2 <1 orw<-1, cs2≥1 give less ISW than cosmological constant Weller, Lewis: astro-ph/0307104 Bean, Doré: astro-ph/0307100 No simple theoretical model gives a very low quadrupoleThe low value is not that unlikelyin a realisation of a standard model

  11. P(k) on smaller scales Bridle, Lewis, Weller, Efstathiou: astro-ph/0302306

  12. Asymmetry of low multipoles? after Eriksen et al astro-ph/0307507:l <~31 shows unlikely asymmetry:evaluate binned Cl on half sky as a function of axis: the lowest ratio of power on opposite two halves is small compared to simulations. Low power in N ecliptic hemisphere. Also astro-ph/0307282 find quadrupole and octopole alignment is unlikely at 1/60 level

  13. WMAP is great, but… • Foreground uncertainties significant at low l – e.g. different analyses of TE power spectrum. Foreground uncertainties not included in likelihoods • Pseudo-Cl estimators combined with maximum likelihood error bars not strictly correct • Noise not included in TT likelihood at l<100, even though larger at l~<100 than l>~100 • Significant correlation between TT and TE power spectra neglected – bias on e.g. • Likelihood approximation not valid for outlier points • Is it valid to do parameter estimation with usual assumptions when Cl not consistent with Gaussian expectations? Do outliers bias results? ... Versions of TE power spectrum

  14. Conclusions • Standard ΛCDM cosmology fits the overall shape of the WMAP power spectrum and is consistent with other data • Low quadrupole is not that unlikely in standard models, but favours models predicting low values by factor <~ 10 • Outlier points/asymmetries – quite strong evidence for analysis problems, foregrounds, or new physics • Parameter constraints from naïve analysis may be misleading – should really understand unexpected features first.

  15. In two bins… 1<l<18 17<l<31

  16. No power in northern hemisphere 3-point function? Measured and marginalized errors from simulations: Eigenmodes:

More Related