Dark Atoms and Puzzles of Dark Matter Searches
  The nonbaryonic dark matter of the Universe is assumed to consist of new
stable forms of matter. Their stability reflects symmetry of micro world and
particle candidates for cosmological dark matter are the lightest particles
that bear new conserved quantum numbers. Dark matter candidates can appear in
the new families of quarks and leptons and the existence of new stable charged
leptons and quarks is possible, if they are hidden in elusive "dark atoms".
Such possibility, strongly restricted by the constraints on anomalous isotopes
of light elements, is not excluded in scenarios that predict stable double
charged particles. The excessive -2 charged particles are bound in these
scenarios with primordial helium in O-helium "atoms", maintaining specific
nuclear-interacting form of the dark matter, which may provide an interesting
solution for the puzzles of the direct dark matter searches.
