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.
