DARK MATTER AND COSMOLOGICAL QCD PHASE TRANSITION

Abstract

In this talk, we take the wisdom that the cosmological QCD phase transition, which happened at a time between 10−5 sec and 10−4 sec or at the temperature of about 150 MeV and accounts for confinement of quarks and gluons to within hadrons, would be of first order, i.e., would release latent "heat" or latent energy. I wish to base on two important points, i.e. (1) that we have 25% dark matter in the present Universe, and (2) that when the early universe underwent the cosmological QCD phase transition it released 1.02 × 10gm/cm3 in latent energy huge compared to 5.88 × 109 gm/cm3 radiation (photon) energy, to deduce that the two numbers are in fact closely related. It is sufficient to approximate the true QCD vacuum as one of degenerate θ-vacua and can be modelled effectively via a complex scalar field with spontaneous symmetry breaking. We examine how "pasted" or "patched" domain walls are formed, how such walls evolve in the long run, and we believe that the majority of dark matter could be accounted for in terms of such domain-wall structure and its remnants. The latent energy released due to the conversion of the false vacua to the true vacua, in the form of "pasted" or "patched" domain walls at first and their evolved objects, make it obsolete the "radiation-dominated" epoch or later on the "matter-dominated" epoch.