Another look at Gaussian isocurvature hot dark matter models for large-scale structure

We examine Gaussian isocurvature hot dark matter (massive neutrino) models for large-scale structure in which the initial density perturbations are produced in the baryons with a power-law spectrum P-B(k) = Ak(nB). We calculate the linearly evolved power spectrum and cosmic microwave fluctuations. We find the models with only isocurvature perturbations are inconsistent with observations of damped Ly alpha systems and COBE constraints on the power index. However, models that contain a mixture of adiabatic and isocurvature perturbations can be made consistent with COBE, galaxy surveys, and damped Ly alpha systems. Isocurvature hot dark matter models also produce a bias between baryons and neutrinos even in the linear regime. We find that this ''natural bias'' can increase the baryon fraction in small-scale objects like damped Ly alpha systems, but it has no effect on cluster scales.