Open and closed CDM isocurvature models contrasted with the CMB data

We consider pure isocurvature cold dark matter models in the case of open and closed universe. We allow for a large spectral tilt and scan the 6-dimensional parameter space for the best fit to the COBE, Boomerang, and Maxima-1 data. Taking into account constraints from large-scale structure and big bang nucleosynthesis, we find a best fit with $\chi^2 = 121$, which is to be compared to $\chi^2 = 44$ of a flat adiabatic reference model. Hence the current data strongly disfavour pure isocurvature perturbations.