Motivated by the recent measurement of the primeval abundance of deuterium , we re-examine the nuclear inputs to big-bang nucleosynthesis ( BBN ) .
Using Monte-Carlo realization of the nuclear cross-section data to directly estimate the theoretical uncertainties for the yields of D , ^ { 3 } He and ^ { 7 } Li , we show that previous estimates were a factor of 2 too large .
We sharpen the BBN determination of the baryon density based upon deuterium , \rho _ { B } = ( 3.6 \pm 0.4 ) \times 10 ^ { -31 } { g cm ^ { -3 } } ( \Omega _ { B } h ^ { 2 } = 0.019 \pm 0.0024 ) , which leads to a predicted ^ { 4 } He abundance , Y _ { P } = 0.246 \pm 0.0014 and a stringent limit to the equivalent number of light neutrino species : N _ { \nu } < 3.20 ( all at 95 % cl ) .
The predicted ^ { 7 } Li abundance , ( ^ { 7 } Li/H ) _ { P } = 3.5 ^ { +1.1 } _ { -0.9 } \times 10 ^ { -10 } , is higher than that observed in pop II stars , 1.7 \pm 0.3 \times 10 ^ { -10 } ( both , 95 % cl ) .
We identify key reactions and the energies where further work is needed .