** Authors:**
KORAY KARACA, SELÇUK BAYIN

** Abstract: **
In the light of recent observations which point to an open
universe (\Omega _{0} < 1), we reconsider singularity-free models,
originally constructed for closed universes. Our model starts from a
nonsingular state called prematter, governed by an inflationary
equation of state P=( \gamma _{p}-1) \rho , where \gamma
_{p} is a small positive parameter representing the initial vacuum
dominance of the universe. Unlike the closed models, an open universe
cannot be initially static hence, starts with an initial expansion
rate represented by the initial value of the Hubble constant H(0).
Therefore, our model is a two-parameter universe model (\gamma
_{p},H(0)). During the prematter phase, due to the unusual
characteristic of the equation of state, the universe heats up even
though it expands. When the temperature in the universe reaches the
Planck temperature T_{pl}, which is taken as the maximum attainable
physical temperature, a first order phase transition carries the
universe into the radiation era. Then the universe starts to behave
as predicted in the standard model. The model proposed in this work
predicts a value between 60 and 80 Km\cdot \sec ^{-1}\cdot Mpc^{-1}
for the present value of the Hubble constant H_{0}, and the predicted
value of \Omega _{0} lies between 0.3 and 0.6. Comparing the
predictions of this model for the present properties of the universe
with the recent observational results, we argue that the model
constructed in this paper could be used as a realistic universe model.

** Keywords: **

** Full Text:** PDF