2,263 research outputs found
Quark-Hadron Phase Transitions in Viscous Early Universe
Based on hot big bang theory, the cosmological matter is conjectured to
undergo QCD phase transition(s) to hadrons, when the universe was about s old. In the present work, we study the quark-hadron phase transition, by
taking into account the effect of the bulk viscosity. We analyze the evolution
of the quantities relevant for the physical description of the early universe,
namely, the energy density , temperature , Hubble parameter and
scale factor before, during and after the phase transition. To study the
cosmological dynamics and the time evolution we use both analytical and
numerical methods. By assuming that the phase transition may be described by an
effective nucleation theory (prompt {\it first-order} phase transition), we
also consider the case where the universe evolved through a mixed phase with a
small initial supercooling and monotonically growing hadronic bubbles. The
numerical estimation of the cosmological parameters, and for instance,
makes it clear that the time evolution varies from phase to phase. As the QCD
era turns to be fairly accessible in the high-energy experiments and the
lattice QCD simulations, the QCD equation of state is very well defined. In
light of this, we introduce a systematic study of the {\it cross-over}
quark-hadron phase transition and an estimation for the time evolution of
Hubble parameter.Comment: 27 pages, 17 figures, revtex style (To appear in Phys. Rev. D). arXiv
admin note: text overlap with arXiv:gr-qc/040404
Thermodynamics in the Viscous Early Universe
Assuming that the matter filling the background geometry in the Early
Universe was a free gas and no phase transitions took place, we discuss the
thermodynamics of this closed system using classical approaches. We found that
essential cosmological quantities, such as the Hubble parameter , the
scaling factor and the curvature parameter , can be derived from this
simple model. The results are compatible with the Friedmann-Robertson-Walker
model and Einstein field equations. Including finite bulk viscosity coefficient
leads to important changes in the cosmological quantities. Accordingly, our
picture about evolution of the Universe and its astrophysical consequences
seems to be a subject of radical revision. We found that strongly depends
on thermodynamics of the cosmic background matter. The time scale, at which
negative curvature might take place, depends on the relation between the matter
content and the total energy. Using quantum and statistical approaches, we
introduced expressions for and the bulk viscosity coefficient.Comment: 15 pages, 4 eps figures, invited talk given at the "Second
IAGA-Symposium", Cairo-Egypt, 4-8 Jan. (2010
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