Cold Dark Matter Isocurvature Perturbations: Cosmological Constraints and Applications

TL;DR

This paper constrains cold dark matter isocurvature perturbations using cosmological data, finding they are limited to less than 14.6%, and explores their impact on cosmological parameters and WMAP priors.

Contribution

It provides the first comprehensive constraint on CDM isocurvature contributions using combined astronomical data and analyzes their effects on cosmological parameters.

Findings

Isocurvature contributions are less than 14.6% at 95% confidence.

Mixed adiabatic and isocurvature modes fit data slightly better than pure adiabatic.

Presence of isocurvature modes significantly shifts WMAP normalization parameters.

Abstract

In this paper we present the constraints on cold dark matter (CDM) isocurvature contributions to the cosmological perturbations. By employing Markov Chain Monte Carlo method (MCMC), we perform a global analysis for cosmological parameters using the latest astronomical data, such as 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) observations, matter power spectrum from the Sloan Digital Sky Survey (SDSS) luminous red galaxies (LRG), and "Union2" type Ia Supernovae (SNIa) sample. We find that the correlated mixture of adiabatic and isocurvature modes are mildly better fitting to the current data than the pure adiabatic ones, with the minimal $\chi^2$ given by the likelihood analysis being reduced by 3.5. We also obtain a tight limit on the fraction of the CDM isocurvature contributions, which should be less than 14.6% at 95% confidence level. With the presence of the isocurvature modes, the adiabatic spectral index becomes slightly bigger, n_s^{\rm adi}=0.972\pm0.014~(1\,\sigma), and the tilt for isocurvature spectrum could be large, namely, the best fit value is n_s^{\rm iso}=3.020. Finally, we discuss the effect on WMAP normalization priors, shift parameter R, acoustic scale l_A and z_{*}, from the CDM isocurvaure perturbation. By fitting the mixed initial condition to the combined data, we find the mean values of R, l_A and z_{*} can be changed about 2.9\sigma, 2.8\sigma and 1.5\sigma respectively, comparing with those obtained in the pure adiabatic condition.