Theoretical Studies of Cosmic QCD Phase Transition and Primordial Nucleosynthesis.

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The universe is presumed to have experienced a phase transition from the quark-gluon plasma phase to the hadron gas phase in <approximately equal> 10 musec after the big-bang. We studied theoretically the time evolution of the baryon number density during the cosmic QCD phase transition which has a potential possibility of creating the inhomogeneous universe in baryons. We also studied the primordial nucleosynthesis which took place in a couple of minutes after the phase transition in order to look for several observational evidence of the inhomogeneous cosmolThere are three microscopic parameters in QCD. They are the coexistence temperature of the two phases, T_C, the surface tension of the phase boundary, sigma, and the baryon penetrability through the phase boundary. We applied the chromoelectric flux tube model to the calculation of the baryon penetration rate. This flux tube model is an effective model of quark confinement in QCD and enjoys success for high energy jet phenomenolog … More y. We found that the penetration rate is several orders of magnitude smaller than the previous value which was estimated from a geometrical consideration in an equilibrium condition. As for T_C and sigma, the lattice QCD simulations give the constraints of 100<T_C<250MeV and sigma<10^7MeV^3.We applied the result above to the time evolution of baryon number densities in the two phases during the epoch of the cosmic QCD phase transition. The results are summarized as : 1) If 150<T_CMeV, then the baryon number density distribution is close to the homogeneous one. 2) If T_C<150MeV and 10^5<sigma<10^7MeV^3, then the density distribution is strongly inhomogeneous, leading to a different primordial nucleosynthesis from the standard model. 3) If 100<T_C<150McV and sigma <10^5MeV^3, then the high baryon number density can reach the nuclear matter density or more and the primordial strange quark matter can be formed.In the second case above, the inferred universal baryonic mass density parameter OMEGA is not very far from unity, suggesting that the closed universe, which satisfies the requirement from the inflationary cosmology, is to be realized by baryonic mass alone. The additional hydrodynamical process of homogenization is needed to infer this conclusion. In the third case above, we also found that the created strange quark matter survived evaporation into nucleons in the hot early universe if they include the baryon number larger than 10^<39>. Less