Dark atoms with nuclear shell: a status review

Among dark atom scenarios, the simplest and most predictive one is
that of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O$^{--}$ is bound
to a primordial helium nucleus, and is the main constituent of dark matter. The OHe cosmology has several successes: it leads to a Warmer-than-Cold-dark-matter
scenario for Large-Scale-Structure formation, it can provide an explanation for the excess in positron annihilation line in the galactic bulge and it may explain the
results of direct dark-matter searches. This model liberates
the physics of dark atoms from many unknown features of new physics, but it is still not free from astrophysical uncertainties. It also
demands a deeper understanding of the details of known nuclear and atomic physics, which are still somewhat
unclear in the case of nuclear interacting ``atomic'' shells. These potential problems of the O-helium scenario are also discussed.