Primordial QCD Matter 2014

As the early Universe expanded and cooled down, it is likely to expect that the cosmological background matter should undergo a series of symmetry-breaking/restoring phase transitions, at which various topological defects may have formed. The study of phase transition(s) from quark-gluon plasma (QGP) to hadrons in early Universe dates back to about three decades ago. Absolving inflation and electroweak eras, a first-order phase transition in various scenarios is assumed to take place in the QCD matter. The lattice QCD provides us with an accurate tool to study - among others - the thermodynamics of the strongly interacting matter, for example, the QGP critical temperature and order of the phase transition. The extreme conditions in the early Universe, like high temperatures, high densities and out–of–thermal and –chemical equilibrium, likely affect the properties of the partonic matter. We so far have no access to study this issue. The dissimilarity between the heavy-ion collisions (lattice QCD) and the early Universe in order of the phase transition would be strengthened by the fact that the QGP era seems not to be followed by an extreme expansion (inflation). This is apparently the case in heavy-ion collisions, because of the baryon number conservation and the limitation of baryon-to-photon ratio. The QGP era seems to be the last symmetry breaking of strongly interacting matter. With this statement, we mean deconfinement and chiral symmetry breaking and/or restoring. The discovery and detection of ultra high-energy cosmic rays (UHECR) of energy up to 10-t0-20 eV have posed a serious challenge to the astrophysicists about their origin as well as the physical acceleration mechanisms. Therefore, they impose some interesting and challenging questions as their origin and physical acceleration mechanisms are not entirely known