Browsing by Author "Walia, Parampreet Singh"

We study the possible initial conditions of the universe and the possibility of isocurvature perturbations in the early universe through CMB data. We consider three isocurvature modes; Cold Dark Matter Density Isocurvature (CDI) mode, Neutrino Density Isocurvature (NDI) mode and Neutrino Velocity Isocurvature (NVI) mode. We use three CMB datasets WMAP, QUaD and ACBAR data to constrain the (possibly) correlated adiabatic and isocurvature models. For CDI and NDI models we use both a phenomenological approach, where primordial perturbations are parametrized in terms of amplitudes at two different scales, and a slow-roll two-field inflation approach. For the NVI model we only use the phenomenological approach, since NVI mode would occur only after neutrino decoupling, i.e., after inflation. We find that larger isocurvature fractions are allowed in NDI and NVI models than in corresponding CDI models. For generally correlated perturbations, we find the upper limit to the CDM density, neutrino density and neutrino velocity isocurvature fraction to be 4.5%, 9.8% and 12.4% respectively at k = 0.002 Mpc−1 . Analysis has also been done for the special cases of uncorrelated and fully (anti) correlated perturbations. We find no clear preference for non-zero isocurvature fraction for the models considered. We find that the odds for a correlated isocurvature model compared to the standard adiabatic model are very low. We conclude that the present data does support the standard adiabatic model.