Cold dark matter isocurvature perturbations: Cosmological constraints and applications

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, 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, luminous red galaxies, and the Union2 type Ia supernovae sample. We find that the correlated mixture of adiabatic and isocurvature modes is slightly favored by the current observational data. 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, ${n}_{s}^{\mathrm{adi}}=0.972\ifmmode\pm\else\textpm\fi{}0.014$ ($1\ensuremath{\sigma}$), and the tilt for isocurvature spectrum could be large, namely, the best fit value is ${n}_{s}^{\mathrm{iso}}=3.020$. Finally, we discuss the effect on WMAP normalization priors, shift parameter $R$, acoustic scale ${l}_{A}$, and ${z}_{*}$, from the CDM isocurvature 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 $2.9\ensuremath{\sigma}$, $2.8\ensuremath{\sigma}$, and $1.5\ensuremath{\sigma}$ respectively, comparing with those obtained in the pure adiabatic condition.