BBN with light dark matter
  Effects of light millicharged dark matter particles on primordial
nucleosynthesis are considered. It is shown that if the mass of such particles
is much smaller than the electron mass, they lead to strong overproduction of
Helium-4. An agreement with observations can be achieved by non-vanishing
lepton asymmetry. Baryon-to-photon ratio at BBN and neutrino- to-photon ratio
both at BBN and at recombination are noticeably different as compared to the
standard cosmological model. The latter ratio and possible lepton asymmetry
could be checked by Planck. For higher mass of new particles the effect is much
less pronounced and may even have opposite sign.
