Constraining nonstandard recombination: A worked example

LANDAU, SUSANA J.; DIEGO HARARI; MATIAS ZALDARRIAGA

PHYSICAL REVIEW D - PARTICLE AND FILDS

American Physical Society

Año: 2001 vol. 63 p. 83505 - 83505

0556-2821

We fit the BOOMERANG, MAXIMA and COBE-DMR measurements of the cosmic microwave background anisotropy in spatially flat cosmological models where departures from standard recombination of the primeval plasma are parametrized through a change in the fine structure constant α compared to its present value. In addition to α we vary the baryon and dark matter densities, the spectral index of scalar fluctuations, and the Hubble constant. Within the class of models considered, the lack of a prominent second acoustic peak in the measured spectrum can be accommodated either by a relatively large baryon density, by a tilt towards the red in the spectrum of density fluctuations, or by a delay in the time at which neutral hydrogen formed. The ratio between the second and first peak decreases by around 25% either if the baryon density Ωbh2 is increased or the spectral index n decreased by a comparable amount, or if neutral hydrogen formed at a redshift z* about 15% smaller than its standard value. We find that the present data are best fitted by a delay in recombination, with a lower baryon density than the best fit if recombination is standard. Our best fit model has z*=900, Ωbh2=0.024, Ωmh2=0.14, H0=49 and n=1.02. Compatible with present data at 95% confidence level 780<z*<1150, 0.018<Ωbh2<0.036, 0.07<Ωmh2<0.3 and 0.9<n<1.2.