Constraints on neutrino density and velocity isocurvature modes from WMAP-9 data

Understand

We use WMAP 9-year and other CMB data to constrain cosmological models where the primordial perturbations have both an adiabatic and a (possibly correlated) neutrino density (NDI), neutrino velocity (NVI), or cold dark matter density (CDI) isocurvature component.

• For NDI and CDI we use both a phenomenological approach, where primordial perturbations are parametrized in terms of amplitudes at two scales, and a slow-roll two-field inflation approach, where slow-roll parameters are used as primary parameters.
• For NVI we use only the phenomenological approach, since it is difficult to imagine a connection with inflation.
• We find that in the NDI and NVI cases larger isocurvature fractions are allowed than in the corresponding models with CDI.