Multiple Main Sequence of Globular Clusters as a Result of Inhomogeneous
  Big Bang Nucleosynthesis
  A new mechanism for enhancing the helium abundance in the blue main sequence
stars of omega Centauri and NGC 2808 is investigated. We suggest that helium
enhancement was caused by the inhomogeneous big bang nucleosynthesis. Regions
with extremely high baryon-to-photon ratios are assumed to be caused by the
baryogenesis. Its mass scale is also assumed to be 10^6 Msun. An example of the
mechanisms to realize these two things was already proposed as the Affleck-Dine
baryogenesis. As the baryon-to-photon ratio becomes larger, the primordial
helium abundance is enhanced. We calculated the big bang nucleosynthesis and
found that there exists a parameter region yielding enough helium to account
for the split of the main sequence in the aforementioned globular clusters
while keeping the abundances of other elements compatible with observations.
Our mechanism predicts that heavy elements with the mass number of around 100
is enhanced in the blue main sequence stars. We estimate the timescales of
diffusion of the enhanced helium and mass accretion in several stages after the
nucleosynthesis to investigate whether these processes diminish the enhancement
of helium. We found that the diffusion does not influence the helium content. A
cloud with a sufficiently large baryon-to-photon ratio to account for the
multiple main sequence collapsed immediately after the recombination.
Subsequently, the cloud accreted the ambient matter with the normal helium
content. If the star formation occurred both in the collapsed core and the
accreted envelope, then the resultant star cluster has a double main sequence.
