A study of the cosmological quark-hadron transition

In this thesis, several aspects of the cosmological quark-hadron transition are studied in detail. A general introduction discusses the importance of phase transitions in the early universe with particular emphasis on the quark-hadron transition and its possible cosmological consequences. In the second chapter we first give a brief review of present knowledge of the quark-hadron transition on the basis of lattice results from quantum chromodynamics. These are then used for a general discussion of the possible large scale cosmological effects of the confinement process. In the following discussion it is assumed that the transition is of first order, as suggested by many lattice computations, and that bubbles of the hadronic phase are nucleated in a supercooled quark medium. Lattice results, however, are not accurate enough to give a reliable equation of state for use in hydrodynamical calculations of bubble growth and so we also discuss phenomenological models which are more convenient. The general relativistic hydrodynamical equations governing the bubble growth are presented in detail in Chapter III. Particular attention is devoted to the characteristic formulation of the hydrodynamical equations and to a correct specification of the junction conditions at the phase interface. For the latter, Israel's method for singular hypersurfaces is used to give a proper treatment of surface effects. In Chapter IV a short review of classical bubble dynamics is presented, followed by a description of the characteristic structure of detonation and deflagration solutions. For the deflagration case we point out that it is necessary to specify an extra condition giving the rate of the transition as determined by elementary processes. These considerations are then used for showing some important features of a plane deflagration front. Chapter V is devoted to discussing the numerical integration of the coupled system of hydrodynamical equations, junction conditions and the transition rate equation which together govern the dynamics of bubble growth. are also described. Some results of the computations Some possible effects of long range conduction mechanisms are analysed in Chapter VI. In particular, we discuss the ratio between the hydrodynamical and neutrino fluxes and its relevance for possible baryon concentration. There is then an analysis of how the transition would have proceeded on a large scale if the neutrino flux were the dominant mechanism for transfering energy from the quark phase to the hadron phase. Finally in the Conclusion we summarize some main points and discuss some of their wider implications.