  Standard big bang nucleosynthesis (SBBN) has been remarkably successful, and
it may well be the correct and sufficient account of what happened. However,
interest in variations from the standard picture come from two sources: First,
big bang nucleosynthesis can be used to constrain physics of the early
universe. Second, there may be some discrepancy between predictions of SBBN and
observations of abundances. Various alternatives to SBBN include inhomogeneous
nucleosynthesis, nucleosynthesis with antimatter, and nonstandard neutrino
physics.
