Can a matter-dominated model with constant bulk viscosity drive the accelerated expansion of the universe?

Abstract

We test a cosmological model which the only component is apressureless fluid with a constant bulk viscosity as an explanationfor the present accelerated expansion of the universe. We classifyall the possible scenarios for the universe predicted by the modelaccording to their past, present and future evolution and we testits viability performing a Bayesian statistical analysis using theSCP ``Union'' data set (307 SNe Ia), imposing the second law ofthermodynamics on the dimensionless constant bulk viscouscoefficient ζ̃ and comparing the predicted age of theuniverse by the model with the constraints coming from the oldestglobular clusters.The best estimated values found for ζ̃ and the Hubbleconstant H0 are: ζ̃ = 1.922±0.089 and H0 = 69.62±0.59 (km/s)Mpc−1 with aχ2min = 314 (χ2d.o.f = 1.031). The age ofthe universe is found to be 14.95±0.42 Gyr. We see that theestimated value of H0 as well as of χ2d.o.f arevery similar to those obtained from ΛCDM model using thesame SNe Ia data set. The estimated age of the universe is inagreement with the constraints coming from the oldest globularclusters. Moreover, the estimated value of ζ̃ ispositive in agreement with the second law of thermodynamics (SLT).On the other hand, we perform different forms of marginalizationover the parameter H0 in order to study the sensibility of theresults to the way how H0 is marginalized. We found that it isalmost negligible the dependence between the best estimated valuesof the free parameters of this model and the way how H0 ismarginalized in the present work.Therefore, this simple model might be a viable candidate to explainthe present acceleration in the expansion of the universe.