Cold dark matter models with high baryon content

Recent results have suggested that the density of baryons in the Universe, ΩB, is much more uncertain than previously thought, and may be significantly higher. We demonstrate that a higher ΩB increases the viability of critical-density cold dark matter (CDM) models. A high baryon fraction offers the twin benefits of boosting the first peak in the microwave anisotropy power spectrum and of suppressing short-scale power in the matter power spectrum. These enable viable CDM models to have a larger Hubble constant than otherwise possible. We carry out a general exploration of high-ΩB CDM models, varying the Hubble constant h and the spectral index n. We confront a variety of observational constraints and discuss specific predictions. Although some observational evidence may favour baryon fractions as high as 20 per cent, we find that values around 10 to 15 per cent provide a reasonable fit to a wide range of data. We suggest that models with ΩB in this range, with h ≃ 0.5 and n ≃ 0.8, are currently the best critical-density CDM models.