Deuterium, Big-Bang Nucleosynthesis and the Baryon Density

Abstract:  The amount of deuterium produced in the first few
minutes of the hot big bang is a sensitive probe of entropy
per baryon during the early universe.  High resolution spectroscopic
measurements of the deuterium abundance in high redshift, nearly
pristine abosrption systems place strong constraints on the
primordial deuterium ratio, D/H = 2.8x10^-5 (15% uncertainty)
and the cosmological baryon density Omega_b h^2 = 0.021 +- 0.001
I will highlight the main difficulties and possible systematic
uncertainties in the deuterium measurements, and will compare
the results with the recent constraints from anisotropy measurements
of the cosmic microwave background.