May Heavy hadrons of the 4th generation be hidden in our Universe while   close to detection?
  Metastable quarks of 4th generation are predicted in the framework of heterotic string phenomenology. Their presence in heavy stable hadrons are usually strongly constrained; however their hidden compositions in Heavy doubly charged baryons here considered are found to be still allowable: we studied their primordial quark production in the early Universe, their freezing into cosmic Heavy hadrons, their later annihilation into cosmic ray as well as their relic presence in our Universe and among us on Earth. We discuss also their possible production in present or future accelerators. Indeed if the lightest quarks and antiquarks of the 4th generation are stored in doubly charged baryons and neutral mesons, their lifetime can exceed the age of the Universe; the existence of such an anomalous Helium-like (and neutral Pion-like) stable particles may escape present experimental limits, while being close to present and future experimental test. On the contrary primordial abundance of lightest hadrons of the 4th generation with charge +1 can not decrease below the experimental upper limits on anomalous hydrogen and therefore (if stable) it is excluded. While 4th quark hadrons are rare, their presence may play different and surprising role in cosmic rays, muon and neutrino fluxes and cosmic electromagnetic spectra. Most of these traces are tiny, but just nearly detectable. 
K.Belotsky, D.Fargion, M.Yu.Khlopov, R.V.Konoplich, M.G. Ryskin,   K.I.Shibaev