Big bang nucleosynthesis ( BBN ) and the cosmic microwave background ( CMB ) have a long history together in the standard cosmology .
BBN accurately predicts the primordial light element abundances of deuterium , helium and lithium .
The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density .
Recent CMB anisotropy measurements , particularly the observations performed by the WMAP satellite , examine this concordance by independently measuring the cosmic baryon density .
Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions .
These uncertainties are dominated by systematic errors in nuclear cross sections , however for helium-4 they are dominated by the uncertainties in the neutron lifetime and Newton ’ s G. We critically analyze the cross section data , producing representations that describe this data and its uncertainties , taking into account the correlations among data , and explicitly treating the systematic errors between data sets .
The procedure transforming these representations into thermal rates and errors is discussed .
Using these updated nuclear inputs , we compute the new BBN abundance predictions , and quantitatively examine their concordance with observations .
Depending on what deuterium observations are adopted , one gets the following constraints on the baryon density : \Omega _ { B } h ^ { 2 } = 0.0229 \pm 0.0013 or \Omega _ { B } h ^ { 2 } = 0.0216 ^ { +0.0020 } _ { -0.0021 } at 68 % confidence , fixing N _ { \nu,eff } = 3.0 .
If we instead adopt the WMAP baryon density , we find the following deuterium-based constraints on the effective number of neutrinos during BBN : N _ { \nu,eff } = 2.78 ^ { +0.87 } _ { -0.76 } or N _ { \nu,eff } = 3.65 ^ { +1.46 } _ { -1.30 } at 68 % confidence .
Concerns over systematics in helium and lithium observations limit the confidence constraints based on this data provide .
BBN theory uncertainties are dominated by the following nuclear reactions : d ( d,n ) \mbox { $ { } ^ { 3 } { He } $ } , d ( d,p ) t , d ( p, \gamma ) \mbox { $ { } ^ { 3 } { He } $ } , \mbox { $ { } ^ { 3 } { He } $ } ( \alpha, \gamma ) \mbox { $ { } ^ { 7 } { Be } $ } and \mbox { $ { } ^ { 3 } { He } $ } ( d,p ) \mbox { $ { } ^ { 4 } { He } $ } .
With new nuclear cross section data , light element abundance observations and the ever increasing resolution of the CMB anisotropy , tighter constraints can be placed on nuclear and particle astrophysics .