WMAP 3yr primordial power spectrum
Abstract
We constrain the form of the primordial power spectrum using Wilkinson Microwave Anisotropy Probe (WMAP) 3yr cosmic microwave background (CMB) data (plus other high resolution CMB experiments) in addition to complementary largescale structure (LSS) data: 2dF, Sloan Digital Sky Survey (SDSS), Ly α forest and luminous red galaxy (LRG) data from the SDSS catalogue. We extend the work of the WMAP team to that of a fully Bayesian approach whereby we compute the comparative Bayesian evidence in addition to parameter estimates for a collection of seven models: (i) a scaleinvariant Harrison Zel'dovich (HZ) spectrum; (ii) a power law; (iii) a running spectral index; (iv) a broken spectrum; (v) a power law with an abrupt cutoff on large scales; (vi) a reconstruction of the spectrum in eight bins in wavenumber and (vii) a spectrum resulting from a cosmological model proposed by Lasenby & Doran (LD). Using a basic data set of WMAP3 + other CMB + 2dF + SDSS, our analysis confirms that a scaleinvariant spectrum is disfavoured by between 0.7 and 1.7 units of log evidence (depending on priors chosen) when compared with a powerlaw tilt. Moreover, a running spectrum is now significantly preferred, but only when using the most constraining set of priors. The addition of both Lyα and LRG data independently suggests much lower values of the running index than with basic data set alone, and interestingly the inclusion of Lyα significantly disfavours a running parametrization by more than a unit in log evidence. Overall, the highest evidences, over all data sets, were obtained with a powerlaw spectrum containing a cutoff with a significant log evidence difference of roughly 2 units. The natural tilt and exponential cutoff present in the LD spectrum is found to be favoured decisively by a log evidence difference of over 5 units, but only for a limited study within the bestfitting concordance cosmology.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2007
 DOI:
 10.1111/j.13652966.2007.11778.x
 arXiv:
 arXiv:astroph/0607404
 Bibcode:
 2007MNRAS.381...68B
 Keywords:

 cosmic microwave background;
 cosmological parameters;
 cosmology: observations;
 cosmology: theory;
 largescale structure of Universe;
 Astrophysics
 EPrint:
 5 pages, 5 figures submitted to MNRAS letters