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تسجيل مستخدم جديدCan a matter-dominated model with constant bulk viscosity drive the accelerated expansion of the universe?
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We test a cosmological model which the only component is a pressureless fluid with a constant bulk viscosity as an explanation for the present accelerated expansion of the universe. We classify all the possible scenarios for the universe predicted by the model according to their past, present and future evolution and we test its viability performing a Bayesian statistical analysis using the SCP ``Union data set (307 SNe Ia), imposing the second law of thermodynamics on the dimensionless constant bulk viscous coefficient zeta and comparing the predicted age of the universe by the model with the constraints coming from the oldest globular clusters. The best estimated values found for zeta and the Hubble constant Ho are: zeta=1.922 pm 0.089 and Ho=69.62 pm 0.59 km/s/Mpc with a chi^2=314. The age of the universe is found to be 14.95 pm 0.42 Gyr. We see that the estimated value of Ho as well as of chi^2 are very similar to those obtained from LCDM model using the same SNe Ia data set. The estimated age of the universe is in agreement with the constraints coming from the oldest globular clusters. Moreover, the estimated value of zeta is positive in agreement with the second law of thermodynamics (SLT). On the other hand, we perform different forms of marginalization over the parameter Ho in order to study the sensibility of the results to the way how Ho is marginalized. We found that it is almost negligible the dependence between the best estimated values of the free parameters of this model and the way how Ho is marginalized in the present work. Therefore, this simple model might be a viable candidate to explain the present acceleration in the expansion of the universe.
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We explore the viability of a bulk viscous matter-dominated Universe to explain the present accelerated expansion of the Universe. The model is composed by a pressureless fluid with bulk viscosity of the form zeta = zeta_0 + zeta_1 * H where zeta_0 a
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We present and constrain a cosmological model where the only component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a bulk viscosity coefficient
proportional to the Hubble parameter. The model is constrained using the SNe Ia Gold 2006 sample, the Cosmic Microwave Background (CMB) shift parameter R, the Baryon Acoustic Oscillation (BAO) peak A and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is constrained using the three cosmological tests together (SNe+CMB+BAO) we found: 1.- The model violates the SLT, 2.- It predicts a value of H_0 approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- We obtain a bad fit to data with a chi^2_{min} approx 532. These results indicate that this model is viable just if the bulk viscosity is triggered in recent times.
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production rate we obtain that for created matter of dark matter type we can have a quintessence scenario or a future singularity known as little rip; in dependence of the value of a constant parameter, $eta$, which characterizes the matter production effects. The dimensionless age of this kind of Universe is computed, showing that this number is greater than the standard cosmology value, this is typical of universes with presence of dark energy. The inclusion of baryonic matter is studied. By implementing the construction of the particle production rate for a dissipative fluid by considering two approaches for the expression of the bulk viscous pressure; we find that in Eckart model we have a big rip singularity leading to a catastrophic matter production and in the truncated version of the Israel-Stewart model such rate remains bounded leading to a quintessence scenario. For a non adiabatic dissipative fluid, we obtain a positive temperature and the cosmic expansion obeys the second law of thermodynamics.
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