Bounds on Isocurvature Perturbations from Cosmic Microwave Background and Large Scale Structure Data

We obtain very stringent bounds on the possible cold dark matter, baryon andneutrino isocurvature contributions to the primordial fluctuations in theUniverse, using recent cosmic microwave background and large scale structuredata. In particular, we include the measured temperature and polarization powerspectra from WMAP and ACBAR, as well as the matter power spectrum from the 2dFgalaxy redshift survey. Neglecting the possible effects of spatial curvature,tensor perturbations and reionization, we perform a Bayesian likelihoodanalysis with nine free parameters, and find that the amplitude of theisocurvature component cannot be larger than about 31% for the cold dark mattermode, 91% for the baryon mode, 76% for the neutrino density mode, and 60% forthe neutrino velocity mode, at 2-sigma, for uncorrelated models. On the otherhand, for correlated adiabatic and isocurvature components, the fraction couldbe slightly larger. However, the cross-correlation coefficient is stronglyconstrained, and maximally correlated/anticorrelated models are disfavored.This puts strong bounds on the curvaton model, independently of the bounds onnon-Gaussianity.Comment: 4 pages, 1 figure, some minor corrections; version accepted in PR