Can a matter-dominated model with constant bulk viscosity drive the accelerated expansion of the universe?
Arturo Avelino, Ulises Nucamendi
备注：
31 pages, 12 figures and 2 tables. Accepted to be published in the Journal of Cosmology and Astroparticle Physics. Analysis using the new SCP "Union" SNe Ia dataset instead of the Gold 2006 and ESSENCE datasets and without changes in the conclusions. Added references. Related works: arXiv:0801.1686 and arXiv:0810.0303
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 ζand 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 ζand the Hubble constant Ho are: ζ=1.922 \pm 0.089 and Ho=69.62 \pm 0.59 km/s/Mpc with a χ^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 χ^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 ζis 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.
Note on bulk viscosity as an alternative to dark energy
Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto（波尔图大学空间科学与天体物理研究所）；Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto（波尔图大学理学院物理与天文系）；Programa de Pós-Graduação em Física, Universidade Federal do Maranhão（马拉尼昂联邦大学物理学研究生项目）
