Bounds on isocurvature perturbations from CMB and LSS data

Abstract

We obtain very stringent bounds on the possible cold dark matter, baryon and neutrino isocurvature contributions to the primordial fluctuations in the Universe, using recent cosmic microwave background and large scale structure data. In particular, we include the measured temperature and polarization power spectra from WMAP and ACBAR, as well as the matter power spectrum from the 2dF galaxy redshift survey. Neglecting the possible effects of spatial curvature, tensor perturbations and reionization, we perform a Bayesian likelihood analysis with nine free parameters, and find that the amplitude of the isocurvature component cannot be larger than about 31% for the cold dark matter mode, 91% for the baryon mode, 76% for the neutrino density mode, and 60% for the neutrino velocity mode, at 2-sigma, for uncorrelated models. On the other hand, for correlated adiabatic and isocurvature components, the fraction could be slightly larger. However, the cross-correlation coefficient is strongly constrained, and maximally correlated/anticorrelated models are disfavored. This puts strong bounds on the curvaton model, independently of the bounds on non-Gaussianity.

Figures (1)

• Figure 1: a) the likelihood function of the isocurvature fraction $\alpha$, for three different types of uncorrelated isocurvature modes (i.e., with the prior $\beta = 0$); b) the 1 and 2-$\sigma$ contours of $\alpha$ and the cross-correlated mode coefficient $2 \beta\sqrt{\alpha(1-\alpha)}$, for the CDM isocurvature mode: the small (red) contours are based on all the data, with one flat prior $n_{\rm iso} > 0.6$, while the large (green) ones show the situation before WMAP, with an additional prior $\omega_B < 0.037$; c) same as b) for NID; d) same as b) for NIV. The marginalization is approximated by a maximum likelihood fit of the other parameters for each pair of values $(\alpha, \beta)$.