COLD DARK-MATTER MODELS WITH HIGH BARYON CONTENT

Recent results have suggested that the density of baryons in the Unive rse, Omega(B), is much more uncertain than previously thought, and may be significantly higher. We demonstrate that a higher Omega(B) increa ses the viability of critical-density cold dark matter (CDM) models. A high baryon fraction offers the twin benefits of boosting the first p eak in the microwave anisotropy power spectrum and of suppressing shor t-scale power in the matter power spectrum. These enable viable CDM mo dels to have a larger Hubble constant than otherwise possible. We carr y out a general exploration of high-Omega(B) CDM models, varying the H ubble constant h and the spectral index n. We confront a variety of ob servational constraints and discuss specific predictions. Although som e observational evidence may favour baryon fractions as high as 20 per cent, we find that values around 10 to 15 per cent provide a reasonab le fit to a wide range of data. We suggest that models with Omega(B) i n this range, with h similar or equal to 0.5 and n similar or equal to 0.8, are currently the best critical-density CDM models.