Cosmological Constraints from Current Cmb and Sn 1 a Data : a Brute Force 9 Parameter Analysis

We describe constraints on the " standard " 9 parameter open cold dark matter (CDM) model from the most recent CMB and SN1a data. Our parameters are the densities of CDM, baryons, vacuum energy and curvature, the reionization optical depth, and the normalization and tilt for both scalar and tensor fluctuations. We find that although the possibility of reionization and gravity waves substantially weakens the constraints on CDM and baryon density, tilt, Hubble constant and curvature, allowing e.g. a closed Universe, models with vanishing cosmological constant are still strongly disfavored. The currently most popular cosmological model has of order N = 10 free parameters. Upcoming CMB experiments hold the potential to measure these parameters with unprecedented accuracy (Jungman et al.ever, these papers have also demonstrated the importance of fitting for all N parameters jointly, revealing subtle de-generacies by exploring the full N-dimensional parameter space. Although it is tempting to reduce N by invoking theoretical prejudice for the values of some parameters (the N = 2 case being particularly desirable since it is easy to plot), this tends to give misleadingly small error bars. For this reason, there has been a persistent drive towards larger N when analyzing data. The first analyses based on COBE DMR used N = 2 parameters, the CMB quadrupole normalization Q and the scalar tilt n s of the power spectrum (e. Since then, many dozens of papers have extended this to incorporate more data and parameters, recent work including de Bernardis et al. The most ambitious analysis to date is that of Lineweaver (1998 – hereafter L98), jointly varying N = 6 parameters: n s , Q, the Hubble constant h and the relative densities Ω cdm , Ω b and Ω Λ of CDM, baryons and vacuum energy. Yet even this heroic analysis lacks three well-motivated parameters that should be included in a realistic minimal cosmological model: gravity-wave (tensor) fluctuations, parametrized by a relative quadrupole normalization r and a tilt n t , and the optical depth τ from reionization. In an inflationary context, gravity waves are just as natural as deviations from n s = 1, and we know that τ > 0 since the Universe was reionized before z = 5. It is therefore timely to complete this drive towards larger N by performing a full 9 parameter analysis. This is the purpose of the present Letter. In principle, such an analysis …