We place constraints on the number of relativistic degrees of freedom and on the baryon asymmetry at the epoch of Big Bang Nucleosynthesis ( BBN ) and at recombination , using cosmic background radiation ( CBR ) data from the Wilkinson Microwave Anisotropy Probe ( WMAP ) , complemented by the Hubble Space Telescope ( HST ) Key Project measurement of the Hubble constant , along with the latest compilation of deuterium abundances and H \scriptstyle { II } region measurements of the primordial helium abundance .
The agreement between the derived values of these key cosmological and particle physics parameters at these widely separated ( in time or redshift ) epochs is remarkable .
From the combination of CBR and BBN data , we find the 2 \sigma ranges for the effective number of neutrinos N _ { \nu } and for the baryon asymmetry ( baryon to photon number ratio \eta ) to be 1.7–3.0 and 5.53–6.76 \times 10 ^ { -10 } , respectively .