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Helium preenrichment in the first stars

We show that element diffusion can produce large fluctuations in the initial helium abundance of stars. Diffusion time-scale, which in stellar cores is much larger than the Hubble time, can fall below 10 years in the neutral gas clouds of stellar mass, dominated by collisionless dark matter or with dynamically important radiation or magnetic pressure. Helium diffusion may therefore explain the recent observations of globular clusters, which are inconsistent with initially homogeneous helium distribution.