  Big-bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB)
anisotropy measurements give independent, accurate measurements of the baryon
density and can test the framework of the standard cosmology. Early CMB data
are consistent with the longstanding conclusion from BBN that baryons
constitute a small fraction of matter in the Universe, but may indicate a
slightly higher value for the baryon density. We clarify precisely what the two
methods determine, and point out that differing values for the baryon density
can indicate either an inconsistency or physics beyond the standard models of
cosmology and particle physics. We discuss other signatures of the new physics
in CMB anisotropy.
